Patent Publication Number: US-2013228136-A1

Title: Liquid dispenser

Description:
RELATED APPLICATIONS 
     This is a Continuation Application of PCT/US2011/056897, filed Oct. 19, 2011, which claims priority to U.S. Provisional Patent Application Ser. No. 61/394,616, filed Oct. 9, 2010, both of which are incorporated herein in their entirities. 
    
    
     BACKGROUND 
     The present invention relates to a liquid dispenser, and in particular, to a liquid dispenser and method of using the liquid dispenser to treat domestic animals against fleas, ticks, and other pests. 
     Routine care of a domestic animal generally includes treating the animal against fleas, ticks, and other insects. Fleas can be carriers for worms and various diseases, whereas ticks are the most significant anthropod in transmitting diseases to domestic animals. Unlike fleas, ticks can directly cause a disease or illness in an animal. Ticks are responsible for anemia due to blood loss, dermatosis due to salivary secretions, and ascending tick paralysis due to neurotoxins in the salivary secretions. While ticks remain primarily outdoors, fleas can enter a dwelling and cause problems to an animal both indoors and outdoors. 
     As a result, there have been many different preventative measures developed for protecting a domestic animal against fleas, ticks, and other pests. One such example is a flea or tick collar. The collar is worn around the animal&#39;s neck, but in the case of the flea collar, some researchers suggest the collar is ineffective towards preventing fleas. See www.k9web.com. Other preventative measures can include spraying chemicals both indoors and outdoors to kill fleas and/or flea larvae. However, some chemicals have very low toxicity such that only flea larvae are killed, but adult fleas are unaffected. Another preventative measure is bathing a domestic animal with a flea-killing substance to remove any fleas presently residing on the body of the animal. While “dipping” the animal in the flea-killing substance can cure an immediate flea problem, it does not protect the animal against future flea or tick problems. Other preventative measures include powders and other chemicals that may be applied to an indoor carpet or upholstery, for example, that kill fleas or prevent indoor flea infestations. 
     Another common preventative measure is a substance that is topically applied to the domestic animal. Examples include Advantage® from Bayer Corporation, Frontline® from Merial, Ltd., Knockout® from Virbac AH, Inc., and BioSpot® from Farnam Companies, Inc. The substances are liquids which are applied to the skin of an animal and can kill fleas or ticks on contact. Research has shown that such substances can be selectively toxic to other insects and serve as both a repellant and insecticide. See www.k9web.com. The substances work by disrupting the flea&#39;s nervous system and kill up to 100% of existing fleas within 24 hours of application and continue killing fleas for up to 3 months for dogs and 6 weeks for cats. See http://frontline.us.merial.com/products/products_flplus.asp. 
     While the substances discussed above have proven effective at controlling fleas and ticks on domestic animals, conventional dispensers used for applying the substances are difficult to use. Before applying one of these substances to the animal, the user must first use scissors or another cutting tool to remove an outer package to access a sealed dispenser in which the substance is contained. To access the substance, one end of the sealed dispenser must be bent along a fold. The bent end can be broken away from the remainder of the sealed dispenser or it can remain attached at the fold. Once the one end is bent, however, the substance is free to flow out of the dispenser and be topically applied to the skin of the animal. 
     One problem with this type of known dispenser is the difficulty of simultaneously handling both the dispenser and the animal to be treated. In the case of larger animals, it often takes one person to hold the animal and a second person using both hands to topically apply the substance. If a person attempts to apply the substance alone, the difficulty in maneuvering the dispenser with one hand and maintaining the animal in place with the other often results in some, if not all, of the substance being spilled on the floor or on the person applying it instead of reaching the animal&#39;s skin. 
     As just alluded, another problem with the conventional dispenser is that the user may come into direct contact with the substance. For example, once the end of the dispenser is bent, the substance is free to flow out of the dispenser. If the user is not careful when handling the dispenser, the substance may leak from the open end onto the user&#39;s body or clothing. 
     Also, some animals have heavy coats with large amounts of fur, e.g., a “double coat,” that prevent or block the substance from being applied to the animal&#39;s skin. In such instances, the user may have to rub the substance into the animal&#39;s fur so that the substance reaches the skin. Again, in this case, the user&#39;s skin or clothing comes into direct contact with the substance and this can pose a health risk to the user, especially if the user does not thoroughly wash their skin or clothing after use. Any direct or indirect contact with the substance can be dangerous. Unfortunately, conventional dispensers are not designed to completely eliminate contact with the substance. 
     Thus, what is needed is a liquid dispenser and method of using the dispenser that allows an individual to topically apply a substance to a domestic animal and reduces or eliminates the possibility of the individual being contaminated with the substance. 
     SUMMARY 
     The present invention provides an apparatus for and a method of dispensing liquid from a dispenser onto an animal. The dispenser has a body that defines a chamber in which liquid is held and a plunger movably disposed in the body. In use, a tip of the dispenser is placed on or near the skin of the animal. The plunger is depressed such that gas located in the chamber is compressed. As the plunger is depressed, the plunger pierces a membrane in the body and forms an opening in the membrane. At least some of the liquid held in the chamber is dispensed through an opening of the dispenser onto the skin of the animal. 
     In one form thereof, a method of dispensing a liquid from a dispenser onto an animal is provided. The dispenser has a body that defines a chamber in which liquid is held and a plunger that is movably disposed in the body. The method includes gripping the dispenser with one hand and placing a tip of the dispenser on or near the skin of the animal. A latch of the dispenser can be unlocked by the one hand, which thereby frees the plunger. The plunger can be depressed with the one hand such that at least some of the liquid dispenses through an opening of the dispenser. A second hand can then be used for holding the animal as the user handles the dispenser and dispenses the liquid onto the skin of the animal. 
     In a different embodiment, a liquid dispenser is provided which includes a hollow body having a membrane and a grip member. The liquid dispenser also includes a finger-actuable plunger that is movably disposed in the body such that movement of the plunger pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser. A finger actuable latch is movably coupled to the body and positioned near the finger actuable plunger. Movement of the latch releases the plunger for movement. The finger actuable latch can prevent accidental discharge of the liquid and also serves as a child-resistant mechanism. 
     These embodiments are advantageous because the dispenser can be handled by an individual using only one hand. The finger actuable latch can be released by the same hand that depresses the plunger for dispensing the liquid. This frees the user&#39;s other hand for holding the animal when dispensing the liquid onto the animal&#39;s skin. The dispenser also provides a tactile sensation to the user when the liquid is dispensed. For example, as the user moves the plunger through the body, the membrane in the body offers resistance to the plunger&#39;s movement. The user is able to feel this resistance, and by applying more force to the plunger, the plunger can pierce through the membrane, thereby creating an opening therein for liquid to exit the dispenser. 
     In another embodiment, a method of manufacturing a dispenser is provided. The method includes providing a dispenser body having a chamber and adding liquid to the chamber. A plunger is inserted into the chamber and a substantially airtight seal is formed between the chamber and plunger. The plunger is held at a desired depth within the chamber and a releasable latch engages the plunger to hold the plunger in place until use. 
     In an advantageous embodiment, a liquid dispenser is provided and includes a hollow body having a grip member and a cap coupled to one end of the body. The cap defines a dispensing opening at an end thereof opposite the body. The dispenser also includes a cartridge having a membrane and which is removably disposed in the cap. A finger-actuable plunger is movably disposed in the body such that movement of the plunger pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser. In one form of this embodiment, the cartridge can be replaceable such that, after a single use, the used cartridge is removed and a new cartridge is inserted into the cap. Advantageously, a user can reuse the dispenser repeatedly without having to purchase another dispenser. Instead, the user only replenishes the cartridge, which provides a more economical and environmentally-friendly dispenser. 
     Likewise, an embodiment which includes a method of using the liquid dispenser is provided. The method includes placing a tip of the cap on or near the skin of the animal and depressing the plunger. When the plunger is depressed, air or gas located in a reservoir defined in the cartridge is compressed. Movement of the plunger pierces the membrane in the cartridge and creates an opening in the membrane. The method further includes dispensing at least some of the liquid through a dispensing opening of the cap onto the skin of the animal. Again, the method can include replacing the used cartridge with a new cartridge. To do so, the cap is decoupled from the body and the used cartridge is removed from the cap. A new cartridge can be inserted into the cap and the cap can then be recoupled to the body. The dispenser is then ready for use. 
     In one form of another exemplary embodiment, a liquid dispensing system is provided. The system includes a dispenser and a plurality of cartridges. The dispenser comprises a hollow body having a grip member and a cap coupled to one end of the body. The cap defines a dispensing opening at an end opposite the body. The dispenser also includes a plunger that is movably disposed in the body. Each of the plurality of cartridges has a membrane. The plurality of cartridges is removably and interchangeably received in the cap. 
     In another form thereof, the system includes a dispenser and a plurality of caps. The dispenser comprises a hollow body and a plunger movably disposed in the body. The body has a grip member. Each of the plurality of caps defines a dispensing opening at one end thereof. Also, a membrane is disposed in each cap. The plurality of caps is removably and interchangeably coupled to one end of the body. 
     Advantageously, the present invention provides an easy-to-use liquid dispenser for topically applying a liquid onto the skin of a domestic animal that requires only one hand of the user to handle and dispense the liquid while freeing the user&#39;s other hand to hold the animal. 
     Another advantage is that the stream or spray that is dispensed from the dispenser is driven at high speed to the skin of the animal instead of being merely topically applied. This provides promotes the medication in reaching its intended location, namely, the skin of the animal, which is especially advantageous with double coated animals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned aspects of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1A  is a perspective view of a conventional dispenser topically dispensing a liquid onto a domestic animal; 
         FIG. 1B  is a perspective view of the conventional dispenser of  FIG. 1A  in which the liquid is shown having been undesirably discharged onto the body of the user; 
         FIG. 2A  is a perspective view of a liquid dispenser in accordance with an embodiment of the present invention topically dispensing a liquid onto a domestic animal; 
         FIG. 2B  is a close-up perspective view of the liquid dispenser of  FIG. 2A ; 
         FIG. 3  is an exploded front-elevational view of an embodiment of a liquid dispenser; 
         FIG. 3A  is a cross-sectional view of one embodiment of a plunger of the liquid dispenser of  FIG. 3  taken along lines  3 A- 3 A; 
         FIG. 3B  is a cross-sectional view of a second embodiment of a plunger of the liquid dispenser of  FIG. 3  taken along lines  3 B- 3 B; 
         FIG. 4A  is a perspective view of a liquid dispenser with a finger actuable latch moved to a release position; 
         FIG. 4B  is a perspective view of the liquid dispenser of  FIG. 4A  with its plunger partially depressed into contact with a membrane; 
         FIG. 4C  is a perspective view of the liquid dispenser of  FIG. 4B  with the plunger having pierced the membrane to dispense a liquid; 
         FIG. 5  is a perspective view of a liquid dispenser in a fully depressed position; 
         FIG. 6A  is a perspective view of a liquid dispenser with a different embodiment of a finger actuable latch; 
         FIG. 6B  is a perspective view of the liquid dispenser of  FIG. 6A  with the finger actuable latch removed and the plunger depressed; 
         FIG. 7  is a perspective view of another embodiment of a liquid dispenser; 
         FIG. 8  is an exploded view of the liquid dispenser of  FIG. 7 ; 
         FIGS. 9   a  and  9   b  are cross-sectional views of the liquid dispenser of  FIG. 7  in a before dispensing position, with  FIG. 9   a  showing the cap not yet installed on the dispenser; 
         FIG. 10  is a cross-sectional view of the liquid dispenser of  FIG. 7  in a dispensed position; 
         FIG. 11  is an exploded view of an alternative embodiment of a liquid dispenser; 
         FIG. 12  is a cross-sectional view of the liquid dispenser of  FIG. 11  in a before dispensing position; 
         FIG. 13  is a cross-sectional view of the liquid dispenser of  FIG. 11  in a dispensed position; and 
         FIG. 14  is a perspective view of a disposable cap for a liquid dispenser; 
         FIG. 15   a  is a partial cross-sectional perspective view of the disposable cap of  FIG. 14 ; 
         FIG. 15   b  is a partial cross-sectional perspective view of an alternate embodiment of the disposable cap of  FIG. 14   
         FIG. 16  is a perspective view of the disposable cap of  FIG. 14  coupled to a liquid dispenser; and 
         FIG. 17  is a perspective view of the disposable cap of  FIG. 14  disassembled from the liquid dispenser. 
     
    
    
     Corresponding reference numerals are used to indicate corresponding parts throughout the several views. 
     DETAILED DESCRIPTION 
     The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention. 
     With reference to  FIGS. 1A and 1B , a conventional dispenser  102  for topically applying a flea or tick control substance to an animal  100  is provided. The conventional dispenser  102  is shown being held by one hand  104  of the user while a second hand  106  holds the animal  100 . Other conventional dispensers may require the user to hold the dispenser with both hands, thereby requiring a second person to hold the animal. Alternatively, the animal may be large and therefore require the presence of a second person. Nevertheless, in  FIG. 1B , the user&#39;s second hand  106  is shown with the control substance  108  having leaked or come into contact with the hand  106 . Conventional dispensers, including the one shown in  FIGS. 1A and 1B , can leak or otherwise come into contact with the user&#39;s body or clothing. This is one of several disadvantages associated with conventional dispensers. 
     With reference to  FIG. 2A , an exemplary embodiment of a dispenser is shown. The dispenser  202  is being held by one hand  204  of a user to topically apply a liquid to an animal  200 . The user&#39;s second hand  206  is available to hold the animal  200  while the liquid is being dispensed thereon. 
     As shown in  FIG. 2B , the dispenser  202  includes a body  216 , plunger  210 , and safety latch  212 . The dispenser  202  is capable of being handled with one hand  204  by the user. For instance, one finger  214  (e.g., the thumb) can move the safety latch  212  from a locked position to an unlocked position so that the plunger  210  can be depressed. A second finger  218  (e.g., the middle finger) can hold or wrap around a grip member  208  of the body  216  while a third finger  220  (e.g., the index finger) can hold the dispenser  202  in an upright position. The second finger  218  and third finger  220  provide control over the use of the dispenser  202  to avoid liquid contacting the user&#39;s body or clothing. Once the safety latch  212  has been moved to the unlocked position, the first finger  214  can depress the plunger  210  for dispensing liquid contained within the body  216  onto the animal  200 . After dispensing (i.e., the plunger has moved to a fully dispensed position), the latch  212  can reengage the plunger  210  and lock the plunger  210  in the fully dispensed position. The structural features of the dispenser and their functionality will be better understood with reference to the discussion below. 
     With reference to  FIG. 3 , one embodiment of a liquid dispenser is provided. The dispenser  300  can include a body  302 , a plunger  304 , and a latch  306 . The body  302  includes a grip member or handle  308  which can be held by one hand of the user. The grip member or handle  308  extends from a substantially cylindrically shaped chamber  310 . The chamber  310  can be hollow and include a first opening  316  at one end thereof and a second opening  318  at a second end thereof. In one embodiment, the diameter of the first opening  316  is at least twice the diameter of the second opening  318 . In a different embodiment, however, the diameter of the first opening  316  is substantially the same as the diameter of the second opening  318 . Alternatively, the ratio of the diameters of the first opening  316  to the second opening  318  can be 3:2, 4:3, 3:1, 5:2, or any other desirable ratio. 
     At the second end thereof, the chamber  310  forms a tapered tip  312 . In other embodiments, the tip  312  can be shaped differently. The second opening  318  is defined at the tip  312 . During use, liquid flows from the cylindrical portion  310  of the chamber to the tip  312  and is dispensed through the second opening  318 . At the second opening  318 , the tip  312  can include lips  322  and  324  (as shown in  FIG. 3 ) that define a gap  320  therebetween. The gap  320  can be important, for example, if the user presses the tip  312  firmly against a surface such as an animal&#39;s skin. Liquid can freely exit from the dispenser  300  through the gap  320  formed between the lips  322  and  324  without the tip  312  becoming plugged against the animal. 
     The body  302  can also include a tab  314  that extends from the chamber  310  opposite the grip member  308 . The tab  314  can have a curved shape such that, during use, a first finger of the user&#39;s hand can wrap around the grip member  308  while a second finger, typically an index finger, wraps around the tab  314 . By holding the dispenser  302  at both the grip member  308  and tab  314 , the user is better able to operate the dispenser  302  with a single hand which thereby frees the user&#39;s second hand for holding the animal. 
     The body  302  can be made from plastic or any other material known to the skilled artisan. In one embodiment, the body  302  can be clear or translucent. In this embodiment, liquid contained within the chamber  310  is visible from outside the chamber. Alternatively, the body  302  can be opaque or colored. The body  302  can be formed through an injection molding process such that the grip member  308 , chamber  310 , tip  312 , and tab  314  are integrally formed. In another embodiment, however, it is possible for the grip member  308  and/or tab  314  to be separate parts coupled to the chamber  310 . 
     The plunger  304  of the dispenser  300  can be substantially cylindrical along its length and made of plastic. The plunger  304  can also be made of other materials known to the skilled artisan and is not limited to plastic. At one end of the plunger  304  is a button  326  and at a second end is a needle  328 . The button  326  can have any cross-sectional shape including circular or oval. The needle  328  is elongate and terminates at a sharp or pointed tip  352 . During use, the tip  352  of the needle  328  can pierce a membrane or septum (see  FIGS. 4-5 ) in the chamber  310  of the body  302 . With reference to  FIGS. 3A and 3B , one or more channels  350  can be defined within or about the needle  328 . The one or more channels  350  can extend substantially along the length of the needle  328  such that, during use, liquid can flow along the one or more channels  350  and escape through the chamber  310  without being blocked by the membrane or septum. In  FIG. 3A , the one or more channels  350  has a V-shaped cross-section, whereas in  FIG. 3B  the one or more channels  350  has a curved cross-section. The one or more channels  350 , however, can have any cross-sectional shape and is not limited to the V-shaped or curve-shaped cross-sections of  FIGS. 3A and 3B , respectively. 
     Between the button  326  and needle  328 , the plunger  304  can have a first cylindrical portion  330 , a second cylindrical portion  332 , and a third cylindrical portion  334 . The diameters of the first cylindrical portion  330 , second cylindrical portion  332 , and third cylindrical portion  334  can be substantially the same or different. A groove  336  is defined between the first cylindrical portion  330  and the second cylindrical portion  332 . The groove  336 , as will be explained in detail below, can engage with the latch  306 . A rib  338  can be formed between the second cylindrical portion  332  and third cylindrical portion  334 . The rib  338  has a diameter that is larger than the diameter of the second cylindrical portion  332  and the third cylindrical portion  334 . As will be explained below, when the plunger  304  is inserted into the chamber  310  of the body  302 , the rib  338  can engage an annular rib (not shown). When the rib  338  engages the annular rib, the plunger  304  has reached the fully depressed position (see  FIG. 5 ). 
     Near the tip end  352  of the needle  328 , an inner annular ring  340  and an outer annular ring  342  are disposed. The inner annular ring  340  is spaced from the outer annular ring  342  such that a groove is defined therebetween. A seal member  344 , such as an o-ring, can be placed in the groove between the inner annular ring  340  and outer annular ring  342 . During use, the seal member  344  can prevent liquid from leaking back into the chamber  310 . 
     As described above, the dispenser  300  can further include a latch  306 . In  FIG. 3 , for example, the embodiment of the latch  306  includes a latch body  346  and one or more arms  348  extending therefrom. The one or more arms  348  can be elastic for engaging the groove  336  formed in the plunger  304 . The latch  306  can function as a child-resistant lock, and therefore the dispenser  300  provides enhanced safety to its design. The latch  306  can be made from plastic or any other material known to the skilled artisan. 
     To assemble the dispenser  300 , the tip end  352  of the plunger  304  can be inserted into the first opening  316  of the body  302 . As the plunger  304  is inserted, the rib  338 , which has an outer diameter less than the inner diameter of the cylindrical body  310 , slides freely into the chamber  310 . The plunger  304 , however, is not completely inserted into the body  302 . Instead, the plunger  304  is inserted to a particular depth before the latch  306  is moved into engagement with the plunger  304 . The latch  306  can slide along a curved surface  354  of the grip member  308  before engaging the plunger  304 . To engage or lock the plunger  304 , the fork-like arms  348  of the latch  306  elastically engage the groove  336  of the plunger  304 . The latch  306  can be pulled away from the plunger  304  to disengage the arms  348  from the groove  336 . In alternative embodiments, the latch  306  can include different structure for engaging the plunger  304 . 
     Turning to  FIG. 4A , the dispenser  300  is shown with a portion of the body  302  and plunger  304  removed. The plunger  304  is shown in an undepressed or ready position. In this position, a reservoir  412  is formed between the seal member  344  and membrane  404  in the body  302 . The reservoir  412  can include air or other gas  410  and a liquid  402  to be dispensed. In the undepressed or ready position, the reservoir  412  has a maximum volume. The tip  352  of the needle  328  extends from the plunger  304  into the reservoir  412  such that the tip  352  is oriented towards the membrane  404 . The inner ring  340  of the plunger  304  can contact an annular rib  418  that protrudes radially inward from the chamber  310  of the body  302 . 
     To dispense liquid  402  from the dispenser  300 , the latch  306  is moved in the direction of arrow  406  ( FIG. 4B ) such that the fork-like arms  348  disengage from the groove  336  of the plunger  304 . The curved surface  354  of the grip member  308  can function as a track or channel along which the latch  306  can slide. An arrow  408  ( FIG. 4A ) can be provided on a surface of the latch  306  to instruct a user which way the latch  306  must be moved for disengaging from the plunger  304 . To completely disengage the latch  306  from the plunger  304 , the latch  306  is moved in the direction of arrow  406  until the latch  306  contacts one or more stoppers  414  that protrude from the curved surface  354  of the grip member  308 . In one embodiment, the latch  306  can be removed from the plunger as a separate component. In another embodiment, however, the latch  306  can be slidably coupled to the curved surface  354  of the grip member  308 . 
     Once the latch  306  has been disengaged from the plunger  304 , the plunger  304  is free to be depressed. In  FIG. 4B , the plunger  304  can be depressed in the direction of arrow  416 . A force can be applied to button  326  causing the plunger  304  to move in the direction of arrow  416 . The tip  352  of the needle  328  likewise moves in the direction of arrow  416  until it contacts the membrane  404  of the body  302 . The membrane  404  can be made from an elastic or deformable material that provides a tactile response to the user once the tip  352  contacts the membrane  404 . As shown in  FIG. 4B , as the tip  352  contacts the membrane  404 , the membrane  404  initially resists the movement of the needle  328 . The user therefore must apply additional pressure to the button along the direction of arrow  416  before the tip  352  will pierce the membrane  404 . 
     As the plunger  304  is depressed, the volume of the reservoir  412  decreases. As a result, the air or other gas  410  within the reservoir  412  is compressed between the seal member  344  and the membrane  404 . While the air or other gas  410  compresses within the reservoir  412 , it does not compress severely enough to rupture or tear the membrane  404 . In addition, the compressed air or gas does not resist movement of the plunger  304  along the direction of arrow  416  to the extent that the user is unable to feel when the tip  352  contacts the membrane  404 . In other words, the user receives tactile feedback from the membrane  404  when the tip  352  engages the membrane  404 , and the user feels significantly less resistance or counter force that opposes the depressing movement of the plunger  304  due to the compressed air or gas. The tactile feedback acts as pneumatic cushioning to the user. Thus, the user can easily distinguish the resistance from the compressed air or gas from the resistance encountered when the tip  352  contacts the membrane  404 . 
     With reference to  FIG. 4C , the plunger  304  is depressed further along the direction  416  of arrow such that the needle  328  pierces the membrane  404 . As the needle  328  pierces the membrane  404 , liquid  402  can be dispensed from the dispenser  300 . The liquid  402  can flow along the one or more channels  350  in the needle  328  before exiting through the second opening  318 . As noted above, the air or gas  410  within the reservoir  412  continues to compress as the plunger  304  moves along the direction of arrow  416  such that once the tip  352  pierces the membrane  404 , liquid  402  is dispensed through the second opening  318 . The liquid  402  can exit the dispenser  300  in a jet-like manner which allows the liquid  402  to penetrate or bypass animal fur or hair, for example, and reach the skin of the animal. This is advantageous over conventional dispensers because the user does not have to rub or smear the liquid into the animal&#39;s skin for the animal to receive treatment. As a result, the dispenser can provide a more hygienic and effective way for topically applying flea or tick control medication to a domestic animal. 
     In  FIG. 5 , the plunger  304  is shown having been fully depressed (i.e., the dispensed position) and most of the liquid  402  has been dispensed through the second opening  318 . In this position, the rib  338  of the plunger  304  engages the annular rib  418  of the chamber  310 , thereby preventing the plunger  304  from moving any further along the direction of arrow  416 . In this embodiment, the dispenser  300  can be discarded or recycled. In alternative embodiments, as will be described in more detail below, a replaceable cartridge can be used such that the dispenser  300  is reusable. 
     With reference to  FIGS. 6A-B , the dispenser  300  includes a body  302 , plunger  304 , and latch  600 . The body  302  and plunger  304  include features similar to those described above with reference to  FIGS. 3-5 . The latch  600 , however, is different in how it engages the plunger  304 . Again, the latch  600  can be a child-resistant lock that enhances the safety of the dispenser  300 . Rather than sliding along the curved surface  354  of the grip member  308 , the latch  600  can be rotated in the direction of arrow  604  for releasing the plunger  304  for use. Until the latch  600  is removed, the plunger  304  cannot be depressed. 
     The latch  600  can include a hook  602  that engages the groove  336  defined in the plunger  304 . The groove  336 , for example, can include a lip or raised surface (not shown) which the hook  602  can engage. Alternatively, the hook  602  engages the groove  336  as a press-fit coupling. One skilled in the art can appreciate other ways in which the hook  602  engages the groove  336 . 
     The latch  600  can further include a handle  606  which can be used for pivoting or removing the latch  600  from the plunger  304 . Although in the embodiment of  FIGS. 6A and 6B  the latch  600  is completely removed or disengaged from the plunger, in other embodiments the latch  600  may be hingedly coupled to the plunger  304  whereby the latch  600  is moved to a position which does not interfere with movement of the plunger  304 . The handle  606  is coupled or formed as part of the latch body  616 . The latch body  616  includes a lip  610  and an inner surface  608  which contacts the outer surface of the plunger  304 . For instance, the radius of the latch body  616  is such that the inner surface  608  fits around the first cylindrical portion  330  of the plunger  304 . The latch  600  can be made of plastic which is elastic and durable. 
     To remove the latch  600  from the plunger  304 , a user first pulls the handle  606  along the direction of arrow  604 . The latch  600  can pivot or be removed, and once removed, the latch  600  can be pulled away from the plunger in the direction of arrow  612 . This releases the plunger to be depressed in the direction of arrow  614  for dispensing liquid contained within the body  302 . 
     A different embodiment of a liquid dispenser is provided in  FIGS. 7-10 . The liquid dispenser  700  is operable with a replaceable cartridge  808  ( FIG. 8 ) and therefore can be reused. The liquid dispenser  700  includes a hollow body  702 , a plunger  704 , and a latch  706 . The body  702  can include a chamber portion  710  into which the plunger  704  is inserted. The body  702  also can include a slot or channel  758  defined therein such that a cap  806  for enclosing the cartridge  808  can be coupled thereto. The channel  758  can include a longitudinal portion  760  and a transverse portion  762 . In this embodiment, the cap  806  couples to the body  702  via a bayonet-style or “quick-disconnect” coupling. The cap  806  includes a pin  756  that is first inserted into the longitudinal portion  760  of the channel  758 . The cap  806  or body  702  is then rotated such that the pin  756  then travels through the transverse portion  762  of the channel  758 . In this position, the cap  806  is securely coupled to the body  702 . The cap  806  can be coupled to the body  702  in alternative ways including press-fit, screw-fit, snap-tight engagement and in other ways known to the skilled artisan. 
     The body  702  can include a grip member  708  and handle  714  such that a user can hold the dispenser  700  with a single hand. Meanwhile, the cap  806  can include a thick cylindrical portion  810  and a thin cylindrical portion  812 . A dispensing opening  800  ( FIG. 8 ) can be defined in the thin cylindrical portion  812  such that liquid exits the dispenser  700  through the dispensing opening  800 . The pin  756  for coupling the cap  806  to the body  702  protrudes from a surface of the thick cylindrical portion  810 . Although only one pin  756  is shown in  FIGS. 7 and 8 , there can be more than one pin  756 . In addition, near the dispensing opening  800  of the cap  806 , the thin cylindrical portion  812  can include a first extending lip  722  and a second extending lip  724 . In  FIG. 8 , a plurality of gaps  720  is defined between the first extending lip  722  and second extending lip  724  such that liquid that exits through the dispensing opening  800  can also radially pass through the plurality of gaps  720 . Thus, if the thin cylindrical portion  812  of the cap  806  is pressed firmly against a surface, during a dispensing operation, liquid can be dispensed radially through the plurality of gaps  720  rather than plugging against the surface. 
     The plunger  704  can include a button  726  at one end thereof which is pushed to force liquid out of the dispenser  700 . In addition, the plunger  704  can include a needle  728  at the opposite end thereof. Between the button  726  and tip  752  of the needle  728 , the plunger  704  includes a first cylindrical portion  730 , second cylindrical portion  732 , and third cylindrical portion  734 . A groove  736  that receives the latch  706  is defined between the first cylindrical portion  730  and second cylindrical portion  732  and a rib  738  protrudes from the plunger  704  between the second cylindrical portion  732  and third cylindrical portion  734 . 
     With reference to  FIG. 8 , the latch  706  can include a latch body  746  and fork-like arms  748  for engaging the groove  736  of the plunger  704 . The underside of the latch body  746  defines a pair of channels  804  that can slidably engage a pair of tracks  802  along the curved surface  754  of the grip member  708 . To disengage the latch  706  from the plunger  704  in this embodiment, the latch  706  can be moved along the tracks  802  of the grip member  708  away from the plunger  704 . The arms  748  can be elastic for engaging the plunger  706  such that the arms  748  can be bent outwardly without breaking or cracking as the latch  706  is disengaged from the plunger  704 . 
     To assemble the dispenser  700 , the tip end  752  of the plunger  704  can be inserted to a predefined depth through a first opening  716  defined at one end of the body  702 . The predefined depth is established such that the groove  736  of the plunger  704  remains outside of the chamber portion  710  of the body  702  so that the latch arms  748  can engage the groove  736 . Once the plunger  704  has been inserted into the chamber portion  710  to the predefined depth, the latch  706  can be coupled to the curved surface  754  of the grip member  708 . To do so, the pair of channels  804  of the latch  706  is aligned with the pair of tracks  802  along the curved surface  754 . The latch  706  can be slid along the curved surface  754  until the latch arms  748  engage the groove  736  of the plunger  704 . Alternatively, the latch  706  may not be required to couple to the curved surface  754  of the grip member  708 . Instead, the latch arms  748  can simply be snapped into engagement with the groove  736  of the plunger  704 . 
     The cap  806  defines a hollow body that has a replaceable cartridge  808  disposed therein which is sealed on the top end by a foil  828 . Foil  828  is pierced by needle  752  as the cap is installed on the main body of the dispenser, as can be appreciated by comparing  FIGS. 9   a  and  9   b . This “pre-opening” feature reduces the force required during dispensing. That is, because foil  828  has already been broken as the cap is installed, the dispensing movement is easier to execute, i.e., requires less force. The cartridge  808  can be any shape, but in the illustrated embodiment of  FIGS. 7-10  the cartridge  808  is cylindrical. Likewise, the cartridge  808  can be made of plastic or any other material known to the skilled artisan. However, it should also be understood that in many embodiments it is desirable to have the cartridge or at least the interior portion thereof that contacts the liquid to be made from a metal foil. One reason for this is that many organic liquids that can be housed in the cartridge in accordance with these teachings may solubilize plastic or volatize through the plastic. Further, due to many plastics allowing penetration of UV light, plastic may also allow photo oxidation. Further, some plastics may allow moisture or oxygen to penetrate them and cause problems that a metal foil can avoid. Aluminum is one particularly suitable metal because it is lightweight and easily piercable, although one of skill in the art would recognize other alternatives. At the end of the cartridge opposite foil  828  is a membrane  814 . Like membrane  828 , membrane  814  is piercable, and this can promote safe and hygienic handling of the cartridge  808 . At the same end of the cartridge  808  as the foil  828 , an annular lip or ring  816  protrudes therefrom. The annular lip or ring  816  has an outer diameter that is less than the inner diameter of the cap  806  such that the cartridge  808  can be inserted into the cap  806 . 
     With reference to  FIGS. 8-10 , the cartridge  808  defines an internal reservoir  904  therein. Liquid  906  and air or other gas are contained within the reservoir  904 . The reservoir  904  is defined at one end of the cartridge  808  by the membrane  814  and at the opposite end by a surface  910  of a piston or second plunger  818  ( FIG. 8 ). The second plunger or piston  818  includes a needle  820  having a sharp or pointed tip  822  that protrudes from one end of the second plunger  818  into the reservoir  904 . In this embodiment, the needle  820  is aligned with the membrane  814 . At the end opposite the needle  820 , the second plunger  818  includes a pointed recess  908  ( FIG. 9 ) defined therein for receiving the pointed tip  752  of the plunger  704  during installation of the cap onto the remainder of the device, as discussed above. The second plunger  818  further includes a plurality of grooves  824  ( FIG. 8 ) defined within the circumference or perimeter (depending on the shape of the second plunger) thereof. A plurality of seal members or o-rings  826  can be placed in the plurality of grooves  824  such that the liquid  906  and air or gas cannot leak past the second plunger  818 . As such, the liquid  906  and air or other gas are sealingly contained within the cartridge  808 . 
     To dispense liquid  906  from the dispenser  700 , the latch  706  first is removed or disengaged from the plunger  704 . Once the latch  706  disengages from the plunger  704 , the plunger  704  is free to be depressed toward the cap  806 . As pressure is applied to the button  726 , the plunger  704  likewise moves further into the chamber portion  710  of the body  702  and the needle tip  752  engages the recess  908  defined in the second plunger  818 . The shape of the recess  908  is shown as corresponding to the shape of the tip  752 , but this is not required. Advantageously, the length of the needle  728  is such that the needle  728  does not buckle when the tip  752  engages the recess  908 . The second plunger  818  is movably disposed in the cartridge  808 . Therefore, as the tip  752  engages the recess  908 , movement of the plunger  704  results in concomitant movement of the second plunger  818  in the same direction. Again, the reservoir  904  is substantially or completely airtight and thus as the second plunger  818  is moved toward the membrane  814 , the volume of the reservoir  904  decreases. A decrease in the volume of the reservoir  904  causes the air or other gas to compress. 
     The plunger  704 , which can also be referred to as the first plunger, moves in conjunction with the second plunger  818  at substantially the same speed and acceleration. The first plunger  704  and second plunger  818  can continue to move in the same direction until the tip  822  of the second needle  820  engages the membrane  814 . The membrane  814  can offer little to no resistance to the tip  822  such that the tip  822  easily pierces through the membrane  814 . Alternatively, however, the membrane  814  can have some amount of elasticity such that as the tip  822  contacts the membrane  814 , the user is required to apply additional force to the button  726  before the tip  822  will pierce the membrane  814 . As such, the membrane  814  can provide tactile feedback to the user. 
     As the tip  822  of the second plunger  820  pierces through the membrane  814 , liquid  906  and compressed air or gas are forced out of the cartridge  808 . The liquid  906  is dispensed through the dispensing opening  800  and/or plurality of gaps  720  defined in the cap  806 . One or more channels  902  can be defined in the second needle  820  and extend along a portion of the length of the needle  820 . Liquid  906  can exit the reservoir  904  by flowing along the one or more channels  902  and therefore the liquid  906  is not blocked by the membrane  814 . 
     After use, the cap  806  can be twisted such that the pin  756  travels through the transverse portion  762  of channel  758 . The cap  806  can then be pulled away from the body  702  as the pin  756  travels through the longitudinal portion  760  of channel  758  until the cap  806  is separated from the body  702 . Once the cap  806  is removed from the body  702 , the used cartridge  808  can be removed from the cap  806  and replaced. In this embodiment, everything except the cartridge is reusable, thereby reducing waste and expense to the user. 
     It should also be understood that the cap and cartridge can be formed such that they are not separable from one another. In such embodiments, the entire cap assembly would be a disposable. 
     Another alternative embodiment of the liquid dispenser is shown in  FIGS. 11-13 . The dispenser  1100  comprises structure similar to the dispenser  700  described above. The dispenser  1100  includes a body  1102 , a plunger  1104 , a latch  1106 , and a cap  1112 . The body  1102  has a grip member  1108  and handle  1114  to assist with holding the dispenser  1100  with one hand. A curved surface  1154  of the grip member  1108  can include a pair of tracks  1152  along which a pair of channels  1150  defined in the latch  1106  can move. The body  1102  also includes a chamber portion  1110  through which the plunger  1104  moves. The chamber portion  1110  can have a channel or slot  1158  defined therein which comprises a longitudinal portion and a transverse portion. A pin or tab  1156  protruding from the cap  1112  engages the channel or slot  1158  and forms a bayonet-style or “quick-disconnect” fitting that couples the cap  1112  to the body  1102 . 
     Besides the channels  1150 , the latch  1106  includes a latch body  1146  and fork-like arms  1148 . The fork-like arms  1148  can be elastic for coupling or engaging a groove  1136  defined in the plunger  1104 . The plunger  1104  includes a button  1126  which can be pressed or forced in a dispensing direction (i.e., towards the cap  1112 ). In addition, the plunger  1104  can include a first cylindrical portion  1130 , a second cylindrical portion  1132 , and a third cylindrical portion  1134 . The aforementioned groove  1136  is defined between the first cylindrical portion  1130  and second cylindrical portion  1132  and an annular rib  1138  protrudes radially outward between the second cylindrical portion  1132  and the third cylindrical portion  1134 . At the end opposite the button  1126 , the plunger  1104  has an end surface  1144  rather than a needle (as in the embodiment of  FIG. 8 ). The end surface  1144  can be planar, recessed, protruding, or any other known design. 
     The cap  1112  comprises a thin cylindrical portion  1140  and a thick cylindrical portion  1142 . The pin or tab  1156  protrudes from the thick cylindrical portion  1142 , whereas a dispensing opening  1128  is defined in the thin cylindrical portion  1140 . The dispensing opening  1128  is formed by a first extending lip  1122  and a second extending lip  1124 . A plurality of gaps  1120  are defined between the first extending lip  1122  and second extending lip  1124  such that liquid can exit the dispenser  1100  through either the dispensing opening  1128  or the plurality of gaps  1120 . 
     The cap  1112  defines a hollow cavity into which a replaceable cartridge  1160  can be inserted. The cartridge  1160  can be any shape, but in the illustrated embodiment of  FIGS. 11-13  the cartridge  1160  is cylindrical and is structurally similar to the cartridge  808  of  FIG. 8 . Likewise, the cartridge  1160  can be made of plastic or any other material known to the skilled artisan. At one end of the cartridge  1160  is a membrane  1162  and at the opposite end thereof is a planar surface  1208  ( FIG. 12 ) of a second plunger  1168 . The membrane  1162  is piercable, but can also provide for safe and hygienic handling of the cartridge  1160 . At the end opposite the membrane  1162 , the cartridge  1160  includes an annular lip or ring  1164  that protrudes therefrom. The annular lip or ring  1164  has an outer diameter that is less than the inner diameter of the cap  1112  such that the cartridge  1160  can be inserted into the cap  1112 . 
     The second plunger  1168  is movably disposed in the cartridge  1160 . During assembly, the second plunger  1168  can be inserted into the cartridge  1160  through an opening  1166  ( FIG. 11 ). The second plunger  1168  can be cylindrical or any other known shape. Along the circumference or perimeter of the second plunger  1168 , one or more grooves  1174  are defined therein. One or more seal members  1176 , such as o-rings, can be placed within the one or more grooves  1174 . Therefore, when the second plunger  1168  is disposed in the cartridge  1160 , an airtight reservoir  1200  ( FIG. 12 ) is established between the membrane  1162  and the second plunger  1168 . As such, liquid  1202  and air or other gas contained within the reservoir  1200  are unable to leak past the one or more seal members  1176 . 
     The second plunger  1168  can also include a piercing member  1170 , i.e., a needle, with a tip  1172  for piercing the membrane  1162 . When the second plunger  1168  is assembled with the cartridge  1160 , the piercing member  1170  is oriented towards and aligned with the membrane  1162 . To further assemble the dispenser  1100 , the second plunger  1168  can be press-fit or snapped into the cartridge so long as the second plunger  1168  can move therein. The cap  1112  is coupled to the body  1102  such that the pin or tab  1156  travels through the longitudinal and transverse portions of the channel  1158 . 
     The plunger  1104  can be inserted to a predefined depth through a first opening  1116  of the body  1102 . The predefined depth is established such that the groove  1136  of the plunger  1104  remains outside of the chamber portion  1110  of the body  1102  so that the latch arms  1148  can engage the groove  1136 . Once the plunger  1104  has been inserted into the chamber portion  1110  to the predefined depth, the latch  1106  can be coupled to the curved surface  1154  of the grip member  1108 . To do so, the pair of channels  1150  of the latch  1106  is aligned with the pair of tracks  1152  along the curved surface  1154 . The latch  1106  can be slid along the curved surface  1154  until the latch arms  1148  elastically engage the groove  1136  of the plunger  1104 . Alternatively, the latch  1106  is not required to couple to the curved surface  1154  of the grip member  1108 . Instead, the latch arms  1148  can simply be pressed or snapped into engagement with the groove  1136  of the plunger  1104 . 
     In operation, the latch  1106  is first removed from the plunger  1104 , thereby releasing the plunger  1104  for movement. To dispense the liquid  1202 , the user applies pressure to the button  1126  of the plunger  1104  (also to be referred to as a first plunger) in a direction towards the cap  1112 . As the first plunger  1104  is pressed further into the chamber portion  1110  of the body  1102 , the end surface  1144  of the first plunger  1104  contacts the corresponding end surface  1208  of the second plunger  1168 . As the first plunger  1104  engages the second plunger  1168 , the second plunger  1168  is pushed toward the membrane  1162 . The volume of the reservoir  1200  thereby decreases causing the air or other gas to compress. Further movement of the first plunger  1104  and second plunger  1168  causes the piercing member  1170  to contact the membrane  1162 . If the membrane  1162  is elastic, the user can feel the tip  1172  of the piercing member  1170  contact the membrane  1162 . The tip  1172  can pierce through the membrane  1162  causing liquid  1202  in the reservoir  1200  to dispense therefrom. The liquid  1202  can flow along a plurality of channels  1204  defined along the length of the piercing member  1170 . The compressed air or gas can force the liquid  1202  from the dispenser  1100  in a jet-like manner. Again, the liquid  1202  can dispense through the dispensing opening  1128  or plurality of gaps  1120 . 
     After use, the cap  1112  can be removed from the body  1102  and the used cartridge  1160  removed from the cap  1112 . A new cartridge  1160  can then be inserted into the cap  1112  for use. The dispenser  1100  therefore is reusable, and the user is only required to purchase new cartridges  1160 . Thus, the present embodiment reduces waste and costs to the user. 
     In  FIG. 14 , a different embodiment of a disposable cap  1400  is shown. The cap  1400  can include a thin portion  1402  and a thick portion  1404 . Both the thin portion  1402  and thick portion  1404  can have cylindrical cross-sections, although in other embodiments the cross-section of each portion can vary. The cap  1400  can be made of plastic material such that it is disposed of after use. Other materials can be used for making the cap  1400 , but one of the advantages associated with the cap  1400  is that it is disposable. 
     A dispensing opening  1414  is defined at one end of the cap  1400 . The dispensing opening  1414  is formed by a first extending lip  1406  and a second extending lip  1407 . A plurality of gaps are defined between the first extending lip  1406  and second extending lip  1407  such that liquid can exit the cap  1400  through either the dispensing opening  1414  or the plurality of gaps. 
     At the opposite end of the cap  1400  is one or more latch arms  1410 . Each latch arm  1410  extends from the thick portion  1404  of the cap  1400  and can engage a body of a dispenser. In addition, each latch arm  1410  includes an angled surface  1518  and a latch edge  1516  (see  FIG. 15 ). When the cap  1400  is pressed into engagement with the body of the dispenser, the angled surface  1518  of each latch arm  1410  slides along the surface of the body. The latch arms  1410  are elastic such that as the angled surface  1518  slides along the body, the arms  1410  can bend outward until engaging the body and thus securing the cap to the body. One of skill in the art would appreciate that the latch arms are provided by way of example, and that cap  1400  could define other connectors that removably connect it to the body of the dispenser. 
     In  FIG. 15   a , the cap  1400  encloses or surrounds a cartridge  1500  that defines a reservoir  1502  therein. The cartridge  1500  can be made of aluminum, for example, or other materials including various metals or plastics. A liquid such as a pesticide can be contained within the cartridge  1500 . In addition to liquid, a gas, a second liquid, or a liquid-gas mixture can be contained within the cartridge  1500 . The cartridge  1500  can be cylindrical or various other shapes. 
     The cap  1400  further includes a foil seal  1412  which is disposed adjacent to the latch arms  1410 . The foil seal  1412  provides a liquid-tight seal at one end of the cartridge  1500 , whereas a membrane  1512  forms a liquid-tight seal at the opposite end thereof. The foil seal  1412  and membrane  1512  provide for safe and hygienic handling of the cap  1400 . 
     A plunger  1504  is movably disposed in the cartridge  1500  between the foil seal  1412  and membrane  1512 . The plunger  1504  is shaped such that it slides along the inner wall of the cartridge  1500 . The liquid and/or gas stored within the cartridge  1500  is generally contained between the bottom edge  1522  of the plunger  1504  and the membrane  1512 . The circumference or perimeter of the plunger  1504  can include defined grooves in which a seal  1510  is fitted or molded. The seal  1510  provides a liquid-tight seal between the plunger  1504  and inner wall of the cartridge  1500 . Alternatively, a plurality of o-rings can be assembled in the grooves of the plunger  1504 . 
     A recess  1520  is defined at one end of the plunger  1504 . The recess  1520  is shaped for receiving a tip of a needle or piercing member, typically when the cap is installed, as described above with respect to  FIGS. 9   a - 9   b.  The recess  1520  can have a conical shape or any other desired shape. At an end opposite the recess  1520 , a needle or piercing member  1506  extends from the plunger  1504 . The needle or piercing member  1506  includes a tip  1508  for piercing the membrane  1512 . Although not shown, the needle or piercing member  1506  can also include channels extending substantially the length of the needle or piercing member such that as the membrane  1512  is pierced, liquid and/or gas can flow along the channels and exit the cap  1400  through the dispensing opening  1414 . 
       FIG. 15   b  is shows cap  1400  with an alternate embodiment of the plunger  1504 . Plunger  1504  shown in  FIG. 15   b  is conically shaped, or tapered. The chamber in which plunger  1504  is moved has a corresponding conical shape as shown in  FIG. 15   b  which promotes a more complete dispensation of the liquid. Further, the corresponding conical shapes tend to guide the tip of the plunger  1504  more precisely to a predefined central location and thus provide a more consistent location at which the foil is pierced. In this connection, it would also be possible to use an absorbent material, e.g., lining the end (bottom) of the cap to retain any residual material that is not dispensed. 
     With reference to  FIGS. 16 and 17 , the cap  1400  can be attached to a hollow body  1602  and main plunger  1604  to form a dispenser  1600 . The body  1602  and main plunger  1604  comprise structures similar to the body  1102  and plunger  1104  of  FIG. 11 . In  FIGS. 16 and 17 , for example, the main plunger  1604  includes a button  1610  at one end thereof and a needle  1700  at the opposite end. The needle  1700  comprises a tip  1702  for piercing the foil seal  1412  of the cap  1400  during assembly. The tip has a conical shape complementary to recess  1520 . The body  1602  can include a grip member  1606  and handle  1608 . Although not shown, a finger-actuable safety latch having a structure similar to the latch  1106  of  FIG. 11  can be included. If included, the latch can be a child resistant locking latch. In addition, the latch can be removably coupled to the plunger  1604 . 
     The cap  1400  can be coupled to a first end  1704  of the body  1602 , whereas the plunger  1604  passes through an opening defined at a second end  1706  of the body. To couple the cap  1400  to the body  1602 , the latch arms  1410  are slid into engagement with the body  1602  along the direction of arrow  1901  shown in  FIG. 16 . In particular, the angled surface  1518  of each latch arm  1410  slides along a surface  1710  of the body  1602  (see  FIG. 17 ). Due to the angle of the angled surface  1518  and elasticity of the latch arm  1410 , the latch arm  1410  bends outward as the angled surface  1518  slides along surface  1710 . As the cap  1400  couples to the body  1602 , each latch arm  1410  snaps into or engages an opening  1612  defined in the body  1602 . Once the cap  1400  is coupled to the body  1602 , the cap  1400  cannot be pulled away from the body  1602  as the latch edge  1516  abuts the surface  1710  of the body  1602 . As described above, as the cap  1400  is coupled to the body  1602 , the tip  1702  of the needle  1700  pierces the foil seal  1412  of the cap  1400 . 
     Once the dispenser  1600  is assembled, a user can dispense liquid and/or gas from the cartridge  1500  by applying a force to the button  1610  of the main plunger  1604  in a dispensing direction as shown by arrow  1800  (see  FIG. 16 ). The main plunger  1604  is moved through the body  1602  until the tip  1702  of the needle  1700  engages the recess  1520  of the plunger  1504 . The user may need to apply an additional force to move the main plunger  1604  and plunger  1504  concomitantly in the dispensing direction as indicated by arrow  1800 . As the plunger  1504  moves in the dispensing direction, air within the reservoir  1502  compresses and the needle or piercing member  1506  contacts the membrane  1512 . If the membrane  1512  is elastic, the user can feel the tip  1508  of the needle or piercing member  1506  contact the membrane  1512 . The tip  1508  can pierce through the membrane  1512  causing liquid and/or gas in the reservoir  1502  to dispense therefrom. The liquid can flow along a dispensing channel  1514  defined in the thin portion  1402  of the cap  1400 . 
     After the dispensing operation, the cap  1400  can be removed from the body  1602 . To assist with the removal of the cap  1400 , wings  1408  protrude from the thick portion  1404  of the cap  1400 . A user twists the cap  1400  by rotating the wings  1408  along the direction indicated by arrow  1900  to disengage the latch arms  1410  from the openings  1612  defined in the body  1602 . It can thus be appreciated that the cap is installed in a linear or longitudinal direction with respect to the dispenser body, whereas it is removed in a twisting movement. Importantly, these features allow the cap to be snapped on in a robust manner, tightly, so that it can withstand the dispensing action. In any event, once the latch arms  1410  are disengaged from the openings  1612 , the cap  1400  can be pulled away from the body  1602 . The cap  1400  can be disposed of after use. To perform another dispensing operation, a new cap  1400  is coupled to the body  1602  as described above. In one embodiment, for example, a plurality of caps are provided, each of which is removably and interchangeably coupled to the body. 
     While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 
     The following is a list of preferred embodiments of the invention:
     1. A method of dispensing liquid from a dispenser onto an animal, the dispenser being of the type having a body, a chamber containing the liquid to be dispensed, and a moveable plunger, the method comprising:   

     placing a tip of the dispenser on or near the skin of the animal; 
     depressing the plunger and thereby compressing gas located in the chamber, wherein the depressing causes a piercing member to pierce a membrane and form an opening in the membrane; and 
     dispensing at least some of the liquid through an opening of the dispenser onto the skin of the animal.
     2. The method of embodiment 1, further comprising unlocking the plunger before the depressing step.   3. The method of embodiment 2, wherein the unlocking step comprises disengaging a latch from the plunger.   4. The method of embodiment 3, wherein the unlocking step comprises sliding the latch along a surface of the body.   5. The method of embodiment 2, further comprising using the same finger or thumb for the depressing step and the unlocking step.   6. The method of embodiment 2, wherein one hand of a user performs the depressing step and the unlocking step while the user&#39;s other hand substantially continuously holds the animal.   7. The method of embodiment 1, further comprising locking the plunger in place after it is fully depressed.   8. The method of embodiment 1, further comprising providing tactile feedback to the user during the depressing step, the tactile feedback comprising initial resistance against the depression and a click or snap perceptible to the user when the plunger is fully depressed.   9. The method of embodiment 1, further comprising substantially depleting the liquid from the dispenser.   10. The method of embodiment 1, wherein an entire dose is dispensed in a single stroke of the plunger.   11. The method of embodiment 1, wherein the piercing of the membrane comprises the plunger pushing the piercing member through the membrane.   12. The method of embodiment 11, wherein the piercing member moves in substantially the same direction as the plunger.   13. The method of embodiment 11, wherein as the piercing member pierces the membrane, at least some of the liquid flows through the opening along a channel defined in the piercing member.   14. The method of embodiment 1, further comprising dispensing the liquid from the dispenser at a high velocity.   15. The method of embodiment 1, wherein the depression step provides a tactile sensation to the user.   16. The method of embodiment 1, wherein the plunger is depressed substantially linearly through the body.   17. The method of embodiment 1, further comprising coupling a cap to one end of the body, the cap comprising the dispensing opening through which liquid exits the dispenser, the cap further comprising a cartridge which includes the membrane disposed at one end and a foil at an opposite end.   18. The method of embodiment 17, further comprising inserting the cartridge into the cap.   19. The method of embodiment 17, wherein movement of the plunger causes the piercing member to pierce the membrane in the cartridge and create an opening in the membrane through which liquid can exit.   20. The method of embodiment 19, wherein an end of the plunger pierces the foil in the cartridge.   21. The method of embodiment 17, further comprising contacting the plunger with a piston movably disposed in the cartridge.   22. The method of embodiment 21, further comprising moving the piston and thereby compressing the gas located in the cartridge.   23. The method of embodiment 21, wherein the piercing member extends from the piston and the piercing of the membrane comprises pushing the piercing member through the membrane.   24. The method of embodiment 23, wherein the piercing member is pushed in substantially the same direction as the plunger when the plunger is depressed.   25. The method of embodiment 23, wherein as the piercing member pierces the membrane, at least some of the liquid flows through the opening along a channel defined in the piercing member.   26. The method of embodiment 21, wherein the contacting step comprises moving a tip of the plunger into a recess defined in the piston.   27. The method of embodiment 17, further comprising decoupling the cap from the body after a dispensing operation.   28. The method of embodiment 27, wherein the decoupling step comprises twisting the cap.   29. The method of embodiment 28, wherein the twisting step comprises applying pressure to at least one wing that extends from the cap.   30. The method of embodiment 27, further comprising replacing the cap with a new cap.   31. The method of embodiment 27, further comprising replacing the cartridge with a new cartridge.   32. The method of embodiment 31, wherein the replacing step comprises inserting the new cartridge into the cap such that, after the inserting step, the membrane is disposed adjacent the dispensing opening.   33. The method of embodiment 31, wherein the replacing step comprises removing the cartridge from the cap.   34. The method of embodiment 30, wherein the replacing step comprises coupling the new cap to the body.   35. The method of embodiment 34, wherein the coupling step comprises sliding a pin defined by the new cap through a slot defined in the body.   36. The method of embodiment 17, wherein the dispensing step comprises dispensing at least some of the liquid through a plurality of gaps defined in the cap.   37. The method of embodiment 17, wherein as the cap is coupled to the body, the plunger pierces the foil of the cartridge.   38. The method of embodiment 17, wherein the coupling step comprises engaging a latch arm of the cap with an opening defined in the body.   39. The method of embodiment 38, further comprising aligning the latch arm with the opening and sliding the latch arm along the outer surface of the body until it engages the opening.   40. A method of dispensing a liquid from a dispenser onto an animal, the dispenser being of the type having a body, a chamber containing the liquid to be dispensed, and a moveable plunger, the method comprising:   

     (a) gripping the dispenser with one hand; 
     (b) placing the tip of the dispenser on or near the skin of the animal; 
     (c) unlocking a latch of the dispenser with the one hand and thereby freeing the plunger; and 
     (d) depressing the plunger with the one hand and thereby dispensing at least some of the liquid through the opening.
     41. The method of embodiment 40, wherein step (c) comprises disengaging the latch from the plunger.   42. The method of embodiment 40, further comprising using the same finger or thumb of the one hand during steps (c) and (d).   43. The method of embodiment 40, further comprising the user using a second hand to substantially continuously hold the animal during at least steps (b), (c) and (d).   44. The method of embodiment 43, wherein the one hand substantially continuously holds the dispenser during at least steps (b), (c) and (d).   45. The method of embodiment 40, further comprising locking the plunger in place after it is fully depressed during step (d).   46. The method of embodiment 40, further comprising providing tactile feedback to the user during step (d), the tactile feedback comprising initial resistance against the depression and a click or snap perceptible to the user when the plunger is fully depressed.   47. The method of embodiment 46, wherein the tactile feedback further comprises pneumatic cushioning.   48. The method of embodiment 40, further comprising substantially depleting the liquid from the dispenser.   49. The method of embodiment 40, wherein an entire dose is dispensed in a single stroke of the plunger.   50. The method of embodiment 40, further comprising piercing a membrane of the chamber during step (d) and thereby producing an opening through which the liquid is dispensed.   51. The method of embodiment 50, wherein the piercing of the membrane comprises pushing a piercing member defined by the plunger through the membrane.   52. The method of embodiment 51, wherein the piercing member is moved in substantially the same direction as the plunger.   53. The method of embodiment 51, wherein as the piercing member pierces the membrane, at least some of the liquid flows through the opening along a channel defined in the piercing member.   54. The method of embodiment 40, wherein the liquid comprises a flea or tick treatment.   55. The method of embodiment 40, further comprising dispensing the liquid from the dispenser at a high velocity.   56. The method of embodiment 40, wherein the depression step provides a tactile sensation to the user.   57. The method of embodiment 40, wherein the plunger is depressed linearly through the body.   58. A liquid dispenser, comprising:   

     a hollow body having a grip member extending therefrom; 
     a plunger movably disposed in the body, wherein movement of the plunger pierces a membrane and creates an opening in the membrane for liquid to exit the dispenser; 
     a latch movably coupled to the body and positioned near the plunger, wherein movement of the latch releases the plunger for movement; and 
     the plunger and latch being positioned relative to the grip member such that when a user&#39;s hand grips the dispenser the same finger of the user can actuate the latch and the plunger without releasing the grip member.
     59. The dispenser of embodiment 58, wherein the plunger comprises a needle, the plunger being movable between a first position and a second position, wherein the needle pierces and at least partially extends through the membrane as the plunger is moved from the first position to the second position.   60. The dispenser of embodiment 59, wherein the needle comprises a channel extending at least partially along the length of the needle.   61. The dispenser of embodiment 59, wherein the needle and membrane cooperate during the piercing to form at least one passageway through which liquid can escape from the dispenser.   62. The dispenser of embodiment 61, wherein the at least one passageway is located laterally from the needle.   63. The dispenser of embodiment 59, wherein the body defines a first opening into which the plunger extends and a second opening through which liquid is dispensed.   64. The dispenser of embodiment 63, wherein the membrane is disposed intermediate the first opening and the second opening.   65. The dispenser of embodiment 59, wherein, in the second position, a tip of the needle is located in the body.   66. The dispenser of embodiment 59, wherein, in the first position, liquid is disposed intermediate the plunger and the membrane.   67. The dispenser of embodiment 58, further comprising a sealing member movingly disposed intermediate the body and plunger.   68. The dispenser of embodiment 67, wherein the sealing member comprises an o-ring circumferentially disposed about the plunger.   69. The dispenser of embodiment 58, wherein the membrane is integrally formed with the body.   70. The dispenser of embodiment 69, wherein the body comprises an injection molded component.   71. The dispenser of embodiment 58, wherein the latch is slidable between a first position in which the latch engages the plunger and prevents the plunger from being depressed until the dispenser is ready to be used and a second position in which the latch is disengaged from the plunger and the plunger is thereby released for movement.   72. The dispenser of embodiment 71, wherein the latch comprises an arm that engages a groove disposed in the plunger in the first position.   73. The dispenser of embodiment 58, further comprising a lock which engages the plunger when the plunger reaches the dispensed position and holds the plunger in the second position.   74. The dispenser of embodiment 58, wherein the grip member comprises at least one groove for a finger of the user.   75. The dispenser of embodiment 58, wherein the membrane is deformable.   76. The dispenser of embodiment 58, wherein the body defines a reservoir having the membrane at one end thereof, the plunger having a sealing member movably disposed at a second end of the reservoir.   77. The dispenser of embodiment 76, wherein the reservoir comprises liquid and gas.   78. The dispenser of embodiment 77, wherein, as the plunger moves toward the membrane, the gas is compressed.   79. The dispenser of embodiment 58, wherein the hollow body comprises a cap disposed at one end thereof.   80. The dispenser of embodiment 79, wherein the cap is removably coupleable to the body.   81. The dispenser of embodiment 80, wherein the cap is removably coupleable to the body via a bayonet-style fitting.   82. The dispenser of embodiment 79, wherein the cap defines a dispensing opening.   83. The dispenser of embodiment 79, further comprising a cartridge removably disposed in the cap, the membrane being disposed at one end of the cartridge.   84. The dispenser of embodiment 83, further comprising a piston movably disposed in the cartridge, the piston being operable by the plunger.   85. The dispenser of embodiment 84, wherein movement of the piston pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser.   86. The dispenser of embodiment 84, wherein the piston comprises a piercing member for piercing the membrane.   87. The dispenser of embodiment 86, wherein the piercing member comprises a plurality of channels defined therein.   88. The dispenser of embodiment 87, wherein, as the piercing member pierces the membrane, liquid flows along the plurality of channels and exits the dispenser.   89. The dispenser of embodiment 86, wherein the piercing member comprises a tip oriented towards and aligned with the membrane.   90. The dispenser of embodiment 84, wherein the plunger is substantially aligned with the piston.   91. The liquid dispenser of embodiment 84, wherein, during use, the plunger moves in a dispensing direction and contacts the piston.   92. The liquid dispenser of embodiment 91, wherein, after the plunger contacts the piston, the plunger and piston move substantially together in the dispensing direction.   93. The liquid dispenser of embodiment 91, wherein the plunger includes a needle that contacts the piston.   94. The liquid dispenser of embodiment 93, wherein, during contact, the tip of the needle engages a recess defined in the piston.   95. The dispenser of embodiment 83, wherein the cartridge comprises a foil disposed at an end opposite the membrane.   96. The dispenser of embodiment 83, wherein, before use, the plunger is spaced from the cartridge.   97. A method of manufacturing a dispenser, comprising:   

     providing a dispenser body having a chamber; 
     adding a liquid to the chamber; 
     inserting a plunger into the chamber; 
     forming a substantially airtight seal between the chamber and the plunger; 
     holding the plunger at a desired depth within the chamber; and 
     engaging the plunger with a releasable latch to hold the plunger in place until use.
     98. The method of embodiment 97, wherein the forming a substantially airtight seal step comprises placing an o-ring in a groove of the plunger.   99. The method of embodiment 97, wherein the adding a liquid step is completed before the inserting a plunger step.   100. The method of embodiment 97, further comprising forming a grip member integral with the dispenser body.   101. The method of embodiment 97, wherein the engaging the plunger step comprises engaging an arm of the latch in a groove disposed in the plunger.   102. The method of embodiment 97, further comprising providing the plunger with a piercing member at one end thereof.   103. The method of embodiment 102, wherein the inserting a plunger step comprises sliding the piercing member of the plunger into the chamber.   104. The method of embodiment 97, further comprising forming a reservoir in the chamber, the reservoir defined by a membrane at one end thereof and the airtight seal at a second end of the reservoir.   105. The method of embodiment 104, wherein, as the plunger is inserted into the chamber, air in the reservoir is compressed.   106. The method of embodiment 97, further comprising providing the dispenser body with a membrane integrally formed therein.   107. The method of embodiment 106, wherein, as the plunger is inserted into the chamber, a tip of the plunger is spaced from the membrane.   108. A liquid dispenser, comprising:   

     a hollow body having a grip member; 
     a cap coupled to one end of the body and defining a dispensing opening; 
     a cartridge disposed in the cap, the cartridge having a membrane; and 
     a plunger movably disposed in the body, wherein movement of the plunger pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser.
     109. The liquid dispenser of embodiment 108, wherein the cartridge is removably disposed in the cap.   110. The liquid dispenser of embodiment 108, further comprising a latch movably coupled to the body and positioned near the plunger, wherein movement of the latch releases the plunger for movement.   111. The liquid dispenser of embodiment 110, wherein the grip member comprises a plurality of tracks along which the latch can be moved.   112. The liquid dispenser of embodiment 111, wherein the latch comprises a plurality of channels for movably coupling to the plurality of tracks.   113. The liquid dispenser of embodiment 110, wherein the latch comprises a plurality of fork-like arms for engaging the plunger.   114. The liquid dispenser of embodiment 108, wherein the cap couples to the body via a bayonet-style fitting.   115. The liquid dispenser of embodiment 108, wherein the cap comprises a plurality of latch arms for engaging with openings defined in the body.   116. The liquid dispenser of embodiment 108, wherein the cap comprises a substantially cylindrical portion and a tapered portion, the dispensing opening defined at the tapered portion.   117. The liquid dispenser of embodiment 108, wherein the cap comprises a thin portion and a thick portion, the thin portion defining a dispensing channel through which liquid travels during dispensing.   118. The liquid dispenser of embodiment 108, wherein the cartridge comprises a housing with the membrane disposed at one end thereof.   119. The liquid dispenser of embodiment 108, further comprising a piston movably disposed in the cartridge.   120. The liquid dispenser of embodiment 119, wherein movement of the piston pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser.   121. The liquid dispenser of embodiment 119, wherein the piston comprises a piercing member for piercing the membrane.   122. The liquid dispenser of embodiment 121, wherein the piercing member comprises a plurality of channels defined therein.   123. The liquid dispenser of embodiment 122, wherein, as the piercing member pierces the membrane, liquid flows along the plurality of channels and exits the dispenser.   124. The liquid dispenser of embodiment 121, wherein the piercing member comprises a tip pointed toward the membrane.   125. The liquid dispenser of embodiment 119, further comprising a sealing member disposed intermediate the piston and the cartridge.   126. The liquid dispenser of embodiment 125, wherein the sealing member is disposed in a groove defined in the outer surface of the piston.   127. The liquid dispenser of embodiment 125, wherein the sealing member is molded onto the plunger.   128. The liquid dispenser of embodiment 125, wherein the sealing member comprises an o-ring.   129. The liquid dispenser of embodiment 125, further comprising a reservoir defined by the membrane, the sealing member, and the inner surface of the cartridge.   130. The liquid dispenser of embodiment 129, wherein the reservoir comprises liquid and gas.   131. The liquid dispenser of embodiment 130, wherein the liquid comprises a pesticide for treating animals.   132. The liquid dispenser of embodiment 130, wherein, as the piston moves in a direction towards the membrane, the air in the reservoir is compressed.   133. The liquid dispenser of embodiment 119, wherein the plunger is substantially aligned with the piston.   134. The liquid dispenser of embodiment 119, wherein, during use, the plunger moves in a dispensing direction and contacts the piston.   135. The liquid dispenser of embodiment 134, wherein, after the plunger contacts the piston, the plunger and piston move substantially together in the dispensing direction.   136. The liquid dispenser of embodiment 134, wherein the plunger includes a needle that contacts the piston.   137. The liquid dispenser of embodiment 136, wherein, during contact, the tip of the needle engages a recess defined in the piston.   138. The liquid dispenser of embodiment 134, wherein, after the plunger contacts the piston, at least a portion of the plunger becomes movably disposed in the cartridge.   139. The liquid dispenser of embodiment 108, wherein the dispensing opening is defined at one end of the cap and a foil seal is disposed at the opposite end thereof.   140. The liquid dispenser of embodiment 139, wherein as the cap is coupled to the body, the plunger pierces the foil seal.   141. The liquid dispenser of embodiment 108, wherein the cap is disposable.   142. The liquid dispenser of embodiment 108, wherein the cap comprises a plurality of wings that extend radially outward therefrom.   143. A liquid dispensing system, comprising:   

     a dispenser, comprising: 
     a hollow body having a grip member; 
     a cap coupled to one end of the body, the cap defining a dispensing opening at an end opposite the body; and 
     a plunger movably disposed in the body; and 
     a plurality of cartridges, each cartridge having a membrane and being removably and interchangeably receivable in the cap.
     144. The liquid dispensing system of embodiment 143, wherein the movement of the plunger causes the plunger to pierce the membrane and create an opening in the membrane for liquid to exit the dispenser.   145. The liquid dispensing system of embodiment 143, further comprising a finger-actuable latch movably coupled to the body and positioned near the finger-actuable plunger, wherein movement of the latch releases the plunger for movement.   146. The liquid dispensing system of embodiment 145, wherein the grip member comprises a plurality of tracks along which the latch can move.   147. The liquid dispensing system of embodiment 146, wherein the latch comprises a plurality of channels for movably coupling to the plurality of tracks.   148. The liquid dispensing system of embodiment 145, wherein the latch comprises a plurality of fork-like arms for engaging the plunger.   149. The liquid dispensing system of embodiment 143, wherein the cap couples to the body via a bayonet-style fitting.   150. The liquid dispensing system of embodiment 143, wherein the cap comprises a substantially cylindrical portion and a tapered portion, the dispensing opening defined at one end of the tapered portion.   151. The liquid dispensing system of embodiment 143, wherein the body is substantially transparent.   152. The liquid dispensing system of embodiment 143, wherein the cartridge comprises a housing with the membrane disposed at one end thereof.   153. The liquid dispensing system of embodiment 152, further comprising a piston movably disposed in the cartridge.   154. The liquid dispensing system of embodiment 153, wherein movement of the piston pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser.   155. The liquid dispensing system of embodiment 153, wherein the piston comprises a piercing member for piercing the membrane.   156. The liquid dispensing system of embodiment 155, wherein the piercing member comprises a plurality of channels defined therein.   157. The liquid dispensing system of embodiment 156, wherein, as the piercing member pierces the membrane, liquid flows along the plurality of channels and exits the dispenser.   158. The liquid dispensing system of embodiment 153, further comprising a sealing member disposed intermediate the piston and the cartridge.   159. The liquid dispensing system of embodiment 158, wherein the sealing member is disposed in a groove defined in the outer surface of the piston.   160. The liquid dispensing system of embodiment 158, wherein the sealing member comprises an o-ring.   161. The liquid dispensing system of embodiment 158, further comprising a reservoir defined by the membrane, the sealing member, and the inner surface of the cartridge.   162. The liquid dispensing system of embodiment 161, wherein the reservoir comprises liquid and gas.   163. The liquid dispensing system of embodiment 162, wherein the liquid comprises a pesticide for treating animals.   164. The liquid dispensing system of embodiment 162, wherein, as the piston moves in a direction towards the membrane, the air in the reservoir is compressed.   165. The liquid dispensing system of embodiment 153, wherein the plunger is substantially aligned with the piston.   166. The liquid dispensing system of embodiment 153, wherein, during use, the plunger moves in a dispensing direction and contacts the piston.   167. The liquid dispensing system of embodiment 166, wherein, after the plunger contacts the piston, the plunger and piston move substantially concomitantly in the dispensing direction.   167. The liquid dispensing system of embodiment 166, wherein the plunger includes a needle that contacts the piston.   168. The liquid dispensing system of embodiment 167, wherein, during contact, the tip of the needle engages a recess defined in the piston.   169. The liquid dispensing system of embodiment 166, wherein, after the plunger contacts the piston, at least a portion of the plunger becomes movably disposed in the cartridge.   170. A system for dispensing a liquid or gas, comprising:   

     a dispenser comprising a hollow body and a plunger movably disposed in the body, the body having a grip member; and 
     a plurality of caps, each cap defining a dispensing opening at one end thereof and having a membrane disposed therein, wherein each cap is removably and interchangeably coupleable to one end of the body.
     171. The system of embodiment 170, wherein movement of the plunger causes the plunger to pierce the membrane and create an opening in the membrane for liquid to exit the dispenser.   172. The system of embodiment 170, wherein each cap is coupleable to the body via a bayonet-style fitting.   173. The system of embodiment 170, wherein each cap comprises a latch arm for coupling to the body.   174. The system of embodiment 173, wherein as the cap couples to the body, the latch arm engages an opening defined in the body.   175. The system of embodiment 173, wherein the latch arm comprises a plurality of latch arms.   176. The system of embodiment 170, wherein the cap comprises a thin cylindrical portion and a thick cylindrical portion, the dispensing opening defined at one end of the thin cylindrical portion.   177. The system of embodiment 170, further comprising a cartridge disposed in each cap, the membrane disposed at one end of the cartridge.   178. The system of embodiment 177, further comprising a piston movably disposed in the cartridge.   179. The system of embodiment 178, wherein movement of the piston pierces the membrane and creates an opening in the membrane for liquid to exit the dispenser.   180. The system of embodiment 178, wherein the piston comprises a piercing member for piercing the membrane.   181. The system of embodiment 180, wherein the piercing member comprises a plurality of channels defined therein.   182. The system of embodiment 181, wherein, as the piercing member pierces the membrane, liquid flows along the plurality of channels and exits the dispenser.   183. The system of embodiment 178, further comprising a sealing member disposed intermediate the piston and the cartridge.   184. The system of embodiment 183, wherein the sealing member is molded onto the piston.   185. The system of embodiment 178, wherein, during use, the plunger moves in a dispensing direction and contacts the piston.   186. The system of embodiment 185, wherein, after the plunger contacts the piston, the plunger and piston move substantially concomitantly in the dispensing direction.   187. The system of embodiment 185, wherein the plunger includes a needle that contacts the piston.   188. The system of embodiment 187, wherein, during contact, the tip of the needle engages a recess defined in the piston.   189. The system of embodiment 185, wherein, after the plunger contacts the piston, at least a portion of the plunger becomes movably disposed in the cartridge.   190. The system of embodiment 170, wherein, after use, the cap can be decoupled from the body.   191. The system of embodiment 190, wherein each cap comprises a wing that extends radially outward therefrom.   192. The system of embodiment 191, wherein the wing comprises a plurality of wings.   193. The system of embodiment 191, wherein the wing can be twisted for decoupling the cap from the body.   194. The system of embodiment 170, further comprising a finger-actuable latch movably coupled to the body and positioned near the plunger, wherein movement of the latch releases the plunger for movement.   195. A cap for coupling to a liquid dispenser, comprising:   

     a liquid-tight housing for containing a liquid, the housing defining a dispensing opening at one end thereof and defining a connector for coupling to the dispenser; and 
     a plunger movably disposed in the housing, wherein movement of the plunger pierces a membrane in the cap and creates an opening in the membrane for liquid to exit the cap.
     196. The cap of embodiment 195, wherein the membrane is disposed adjacent to the dispensing opening.   197. The cap of embodiment 195, wherein the plunger comprises a piercing member for piercing the membrane.   198. The cap of embodiment 195, further comprising a recess defined in one end of the plunger.   199. The cap of embodiment 195, further comprising a sealing member disposed between the plunger and the housing.   200. The cap of embodiment 199, wherein the sealing member is molded onto the plunger.   201. The cap of embodiment 195, further comprising a foil seal disposed adjacent to the connector.   202. The cap of embodiment 195, wherein the connector comprises a latch arm.   203. The cap of embodiment 195, further comprising a plurality of wings extending from the housing.   204. The cap of embodiment 195, further comprising a dispensing channel defined within the housing, the channel extending from the membrane to the dispensing opening.