Abstract:
A microscope slide stainer includes a platform that supports a plurality of microscope slides. The platform includes surface areas, heated by resistive heaters, under the microscope slides. A liquid dispenser is located above the platform and the dispenser and platform are adapted for relative movement with respect to each other. The dispenser dispenses liquid reagents onto a slide bearing a biological sample.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a Continuation-in-Part of U.S. application Ser. No. 09/702,298 filed Oct. 31, 2000, which is a Continuation of U.S. application Ser. No. 09/205,945 filed Dec. 4, 1998, now U.S. Pat. No. 6,180,061, which is a Continuation-in-Part of U.S. application Ser. No. 08/887,178, filed Jul. 2, 1997, now U.S. Pat. No. 5,947,167, which is a Continuation-in-Part of U.S. application Ser. No. 08/251,597, filed May 31, 1994, now U.S. Pat. No. 5,645,114, which is a Continuation-in-Part of U.S. application Ser. No. 07/881,397, filed on May 11, 1992, now U.S. Pat. No. 5,316,452, the entire teachings of which are incorporated herein by reference. 
     
    
     GOVERNMENT SUPPORT  
       [0002] The invention was supported, in whole or in part, by a grant 1R43AI29778-02 from Department of Health and Human Services Public Health Service, Small Business Innovation Research Program. The Government has certain rights in the invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    In a field of medical laboratory testing known as histopathology, a disease is diagnosed from a biopsy specimen by microscopic examination of the diseased tissue. Various molecules in a tissue section, mounted on a microscope slide, are colored. By causing the desired molecules to be colored, or “stained” as it is commonly called, their presence or quantity can be detected. The presence or quantity of specific molecules in a tissue biopsy can be important in rendering a diagnosis or determining therapy.  
           [0004]    There are three different types of stains that are generally useful for staining tissue biopsies in this manner. Different stains are used for different purposes, to answer different clinical questions that may be important in determining the diagnosis. These stains are well known in the art. Histochemical stains are comprised of stains or dyes in the nature of chemicals. Examples of histochemical stains include the hematoxylin and eosin stain, periodic acid-Schiff stain, Gram stain, Grocott&#39;s methenamine silver stain, May-Grunwald Giemsa stain, acid fast stain, etc. In each of these stains, various chemicals cause the development of color in the tissue section, if the particular molecule(s) being tested for are present. Another type of stain is known as an immunohistochemical stain (IHC). IHC stains involve an immunologic reaction whereby an antibody detects a particular molecule. The presence of the antibody is then detected using a calorimetric reaction that is visible under microscopic examination. IHC stains are particularly useful for detecting specific types of proteins. A third type of stain is known as in situ hybridization (ISH). ISH stains detect specific nucleic acid sequences through complementary binding of a DNA or RNA probe. The presence of bound probe is then detected through a colorimetric reaction that is visible under microscopic examination. ISH stains are particularly useful for detecting specific genes, or nucleic acid sequences. All of these stains have various uses in the diagnosis of disease.  
           [0005]    As these staining procedures have become increasingly important, instrumentation to automate the processes has been developed. The earliest types of stainers were batch stainers, in that all of the slides were treated in a similar fashion. Commonly performed stains are also called routine stains. The stains performed in batch stainers included the hematoxylin and eosin stain, a routine stain that is commonly performed on most biopsy specimens. Later, stainers were developed that provided flexibility in the staining protocols for the different slides. Namely, different slides in the instrument can be processed according to different staining protocols. This feature is generally referred to in the art as random access. Random access slide stainers are relatively recent developments, as the need for non-routine staining has increased. Non-routine stains are those stains that are typically performed on an as-needed basis, to answer specific clinical questions for the patient biopsy. Immunohistochemical and in situ hybridization stains are typically considered non-routine stains. In addition, many histochemical stains are also considered non-routine, in that they are performed on specific patient samples in order to address a diagnostic question of importance to that patient. In the art, these non-routine histochemical stains are also called “special stains”.  
           [0006]    Many of the non-routine stains, including special stains, immunohistochemical or in situ hybridization stains, call for the application of heat at a certain point in time during the staining procedure. Therefore, when designing instrumentation for performing the stains automatically, it is desirable to provide for the application of heat to the slides.  
         SUMMARY OF THE INVENTION  
         [0007]    In a microscope slide stainer, a platform supports a plurality of microscope slides. The platform has at least one heated surface area heated by a heater thereunder. The heated surface area is in contact with and underlies at least one microscope slide bearing a biological sample. A liquid dispenser dispenses liquid reagents onto the slide bearing the biological sample. The liquid dispenser is located above the platform, and the dispenser and platform are adapted for relative movement with respect to each other.  
           [0008]    The slide stainer may comprise a plurality of heated surface areas, and each heated surface area may support only one slide. A slide support on the platform may have plural heated surface areas, and there may be plural slide supports on the platform.  
           [0009]    A resistive heating element may underlie the heated surface area. To provide the relative movement, either the liquid dispensing station, or the platform, or both may move. In one embodiment, the liquid dispensing station is stationary and the platform moves to index slides to the liquid dispensing station.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0011]    [0011]FIG. 1 is a cross-sectional view of the pump cartridge and dispensing actuator mounted on a frame.  
         [0012]    [0012]FIG. 2 is a perspective view of the pump cartridge reservoir.  
         [0013]    [0013]FIG. 3 is a view from above of the pump cartridge.  
         [0014]    [0014]FIG. 4 is a view from above of a plurality of pump cartridges mounted on a first embodiment dispensing assembly including a rectangular frame and chassis of an X-Y axis robot.  
         [0015]    [0015]FIG. 5 is a perspective view of a dispensing assembly of a second embodiment of the invention.  
         [0016]    [0016]FIG. 6 is a top view of a slide frame for providing five sealed cavities above five different slides holding tissue samples.  
         [0017]    [0017]FIG. 7 is a top view of a slide frame base.  
         [0018]    [0018]FIG. 8 is a top view of a slide frame housing.  
         [0019]    [0019]FIG. 9 is a side cross-sectional view showing the dispensing actuator of the dispensing station and an exemplary cartridge pump being engaged by the dispensing actuator.  
         [0020]    [0020]FIG. 10 is a side cross-sectional view of a rinse device housed in the dispensing station.  
         [0021]    [0021]FIGS. 11A and 11B are side cross-sectional views of a vacuum hose and transport mechanism for removing rinse and reagent from slides contained on the slide rotor.  
         [0022]    [0022]FIGS. 12-14 are cross-sectional views of the uppermost portion of the cartridge reservoir, demonstrating alternative constructions.  
         [0023]    [0023]FIGS. 15 and 16 are longitudinal sectional views of an alternative dispenser pump cartridge embodying the invention.  
         [0024]    [0024]FIG. 17 is a longitudinal sectional view of the metering chamber tubing of the embodiment of FIGS. 15 and 16.  
         [0025]    [0025]FIG. 18 is a cross-sectional view of a valve needle and plate used in the embodiment of FIGS. 15 and 16.  
         [0026]    [0026]FIG. 19A and 19B are side cross-sectional views of the liquid aspiration station of the second embodiment, with the aspiration head in the lowered (FIG. 19A) and raised (FIG. 19B) positions.  
         [0027]    [0027]FIG. 20 is a schematic representation of the individual heaters on the slide rotor and the temperature control boards mounted on the slide rotor.  
         [0028]    [0028]FIG. 21A-D are a schematic diagram of the electronic circuitry of the temperature control board. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    A description of preferred embodiments of the invention follows.  
         [0030]    Referring to FIG. 1, the cartridge pump CP comprises a pump cartridge reservoir  1  in the shape of a cylindrical barrel. The cartridge reservoir  1  has a lower outlet  11  which is directly connected to a metering chamber comprised of a segment of compressible tubing  2 , an inlet valve  3 , and an outlet valve  4 . The distance between the inlet valve  3  and the outlet valve  4 , and the inner diameter of the tubing  2  defines a volume which can be filled with a liquid. A nozzle  5  is placed below the outlet valve  4  for the purpose of decreasing the flow velocity of the liquid. The cartridge reservoir contains a volume of liquid  12  which is sealed from above by a sliding plunger  6 . The cartridge reservoir  1 , inlet valve  3 , outlet valve  4 , plunger  6 , metering chamber  2 , and nozzle  5  are the components of the cartridge pump CP.  
         [0031]    In a first embodiment of a dispensing assembly, the cartridge pump CP rests on a rectangular frame  7  which can be made of plastic. A single rectangular frame  7  can hold a plurality of cartridge pumps CP. The rectangular frame  7  can be removed from the chassis  8  by simply lifting the frame, thereby lifting all the cartridge pumps with it. In this manner, the wetted components can be easily separated from the electromechanical components.  
         [0032]    The first embodiment dispensing assembly further includes dispensing actuators DA. Each dispensing actuator DA comprises a solenoid  9 , arm  22 , and rubber hammer  1 . When an electrical current is applied to the solenoid  9 , the arm  22  extends forcefully, thereby pressing the rubber hammer  10  against the outer wall of the metering chamber tubing  2 . This action deforms the tubing, causing the compressible tubing to assume a compressed shape  2   a . Since the total volume inside the metering chamber between the valves  3  and  4  is decreased, a volume of liquid is expelled in the direction defined by the valves  3  and  4 . In FIG. 1, the valves are shown as allowing fluid in the downward direction only. Since the diameter of the outlet valve  4  leaflets is comparatively narrow relative to the diameter of the tubing  2 , the fluid has a high flow velocity. This results in a forceful squirting of the liquid. This aspect is often undesirable, since it may lead to splattering of the liquid if the object surface of the fluid is situated immediately below. Therefore, the nozzle  5  is placed below the outlet valve  4 . The nozzle has an inner diameter greater than the diameter of the outlet valve  4  leaflets. This aspect causes the high velocity fluid to first accumulate in the space above and within the inner aspect of the nozzle. The liquid thus exits the nozzle  5  at a slower velocity, ideally in a dropwise manner.  
         [0033]    The rubber hammer  10  is also compressible in order to further decrease the flow velocity of the liquid. Most solenoids tend to extend suddenly and forcefully. This results in a very rapid compression of the tubing  2 . In order to decrease this rate of compression, the solenoid arm is fitted with a compressible rubber hammer  10  which absorbs some of the initial force upon impact with the tubing  2 .  
         [0034]    The tubing  2  can be made of silicone rubber, vinyl, polyurethane, flexible polyvinyl chloride (PVC) or other synthetic or natural resilient elastomers. Such types of tubing are commonly used for peristaltic pumps. The valves can be obtained from Vernay Laboratories, Inc., Yellow Springs, Ohio, 45387 (part #VL 743-102).  
         [0035]    When the electrical current is removed from the solenoid  9 , the arm  22  and rubber hammer  10  is retracted from the surface of the tubing  2 . The tubing in the compressed position  2   a  thereby reverts back to its native position  2  because of the resiliency of the tubing. The reversion of the tubing to its native position results in a negative pressure being created within the metering chamber, causing liquid  12  to be drawn from the pump reservoir  1  into the metering chamber. The metering chamber is therefore automatically primed for the next pump cycle.  
         [0036]    Referring to FIG. 2, the outer aspect of the pump cartridge reservoir  1  has longitudinal ridges  13 . These ridges fit into grooves in the frame  7 , see FIG. 1, in a lock and key fashion. Different cartridges are manufactured with different patterns of ridges in order to identify the contents. In this manner, any particular cartridge will fit only into a position of the frame with a corresponding pattern of grooves. This feature will prevent the possibility of the operator placing the cartridge in an unintended position of the frame.  
         [0037]    Referring to FIG. 3, this shows the variety of possible positions for ridges  13  on the outer surface of the pump cartridge reservoir  1 .  
         [0038]    Referring to FIG. 4, this shows the first embodiment of the dispensing assembly comprising a rectangular frame  7  having plurality of slots  14  for cartridge pumps in position on the chassis  8  a different dispensing actuator DA being associated with each cartridge pump CP. The chassis is mounted on a pair of cylindrical bars  15 . In this case one of the bars is threaded and attached to a motor  16 . Alternatively, a cable drive may be provided. The motor can be a conventional stepping motor or servo motor and driven by a computer-generated signal through an electronic interface.  
         [0039]    [0039]FIG. 5 shows a second embodiment  500  of a dispensing assembly in perspective. Generally, the dispensing assembly  500  comprises a substantially circular assembly base  502 , a slide rotor  504  rotatable on the assembly base  502 , a reagent rotor  506  also rotatable on the assembly base, and a dispensing station  508 .  
         [0040]    The slide rotor  504  is driven to rotate by a servo motor (not shown) and carries ten slide frames  510  that are radially asserted into and detachable from it. A top view of single slide frame  510  is shown in FIG. 6. Here, a different slide holding a tissue sample is held in each slide position  512   a - 512   e . The slide frame  510  comprises a slide frame base  514  shown in FIG. 7. The slide frame base includes a plurality of heated areas  516  which underlie each of the slide positions  512   a - 512   e  and incorporate resistive heating elements, not shown. The heating elements are integrally formed in the slide frame base  514 . Electricity for powering the elements is provided into the slide frame  510  from the assembly base  502  via first and second contacts. Further, third and fourth contacts  520  enable temperature sensing of the heated areas via thermocouples also integrally formed in the slide frame base  514 . Adapted to overlay the slide frame base is a slide frame housing  522 . FIG. 8 is a top view of the slide frame housing  522  showing essentially a rigid plastic or metal frame  524  with five oval holes  526   a - 526   e  corresponding to each of the slide positions  512   a - 512   e . A silicon rubber gasket  528  is also provided under the plastic frame  524 . Returning to FIG. 6, the slide frame housing  522 , including the gasket  528  and plastic frame  524 , is bolted onto the slide frame base  514  by two Allen bolts  530  to provide individual sealed cavities approximately 0.2-0.4 inches deep over each tissue sample slide placed at each of the slide positions  512   a - 512   e . As a result, a total of 3 ml of reagents and/or rinses can be placed in contact with the tissue samples of each one of the slides but a maximum quantity of 2 ml is preferable. Since the silicone gasket  528  is compressed by the plastic frame  522  against the slide frame base  514 , the cavities over each of the frame positions are mutually sealed from each other.  
         [0041]    Returning to FIG. 5, above the slide rotor  504  is a non-rotating slide cover  532 . This disk-like structure rides above the slide rotor  504  but does not turn with the slide rotor. Basically, it forms a cover for all of the tissue samples held in each of the slide frames  510  so that evaporation of reagents or rinses contained on the slides can be inhibited and also so that environmental contamination of the tissue samples is prevented.  
         [0042]    Positioned above the slide rotor  504  is the reagent rotor  506 . This reagent rotor  506  is similarly adapted to rotate on the assembly base  502  and is driven by another servo motor (not shown) so that the reagent rotor  506  and slide rotor  504  can rotate independently from each other. The reagent rotor  506  is adapted to carry up to ten arcuate cartridge frames  534 . These arcuate cartridge frames are detachable from the reagent rotor  506  and can be selectively attached at any one of the ten possible points of connection. Each arcuate cartridge frame  534  is capable of carrying five of the reagent cartridge pumps CP. A cross sectional view illustrating the arcuate cartridge frame as shown in FIG. 9. As illustrated, the reagent cartridge pump CP is vertically insertable down into a slot  536  in the arcuate cartridge frame  534  so that the nozzle tip  538  extends down below the cartridge frame and the meter chamber tubing  2  is exposed. The arcuate cartridge frame  534  including any cartridge pumps CP is then slidably insertable onto the reagent rotor  506 .  
         [0043]    Generally, the dispensing station  508  comprises a dispensing actuator DA for engaging the meter chamber tubing  2  of any one of the reagent cartridge pumps CP in any slot in any one of the arcuate cartridge frames  534 . Further, the dispensing station  508  includes rinse bottles  540  that can supply rinses into any one of the slides on any one of the slide frames  510  via rinse tubes  542 , and a rinse removal vacuum  544  including a vacuum tube that is extendable down into any one of the cavities in the slide frames  510  to remove rinse or reagent.  
         [0044]    Specifically, the dispensing station  508  includes a station frame that has a front wall  546  generally following the curvature of the assembly base  502 . The station frame also includes a horizontal top wall  548  continuous with the front wall  546  and from which rinse bottles  540  are hung. The front wall  546  of the station housing supports a single dispensing actuator DA. As best shown in connection with FIG. 9, the dispensing actuator DA includes a solenoid or linear stepping motor  9 , an arm  22 , and a compressible rubber hammer  10  as described in connection with the dispensing actuator illustrated in FIG. 1. Use of a linear stepping motor instead of a solenoid somewhat negates the necessity of the rubber hammer being highly compressible since the rate of extension of linear stepping motors can be controlled to a slow speed. Because only a single dispensing actuator is required in the second embodiment, more expensive alternatives such as the linear stepping motor are preferable. As another possible alternative, the reciprocating hammer of the dispensing actuator could take the form of a cam, driven by a rotary motor, that engages the compressible tubing so that rotation of the cam will deform the compressible tubing.  
         [0045]    Upon actuation of the solenoid  9 , the rubber hammer  10  extends outwardly to engage the compressible tubing  2  of the particular cartridge pump CP that has been rotated into position in front of the dispensing actuator DA on the reagent rotor  504 . The liquid dispensed from the pump cartridge CP by the action of the dispensing actuator DA falls down through a hole  550  formed in the slide cover  532  into the particular medical slide that has been brought into position in front of the dispensing actuator DA by the rotation of the slide rotor  504 . In this way, any one of fifty slides, which the slide rotor  504  is capable of carrying, can be accessed and treated with any one of fifty different reagents that the reagent rotor  506  is capable of carrying in the cartridge pumps CP by properly rotating both the reagent rotor and the slide rotor. By this method both the reagent cartridge pump CP carrying the desired reagent and the slide which the operator intends to receive this reagent are brought to circumferential position of the dispensing actuator DA.  
         [0046]    The dispensing station  508  also carries up to eight different rinses that can be delivered through rinse tubes  542  to any one of the slides held on the slide rotor  504 . As shown in FIG. 10, the rinse bottles  540  are screwed into a female threaded cap  552  secured to the underside of the horizontal top wall  546  of the station frame. Compressed air is from a compressor  554  is provided into each one of the rinse bottles  540 . The pressure above the rinse then enables the rinse to be forced out through the dip tube  556  through rinse hose  558  when a pinch valve  560  is opened. Depending on the length of time that the pinch valve is opened, a predetermined amount of rinse can be provided out through the rinse tube  542  into the particular medical slide that has been brought underneath the rinse tube end  562  by the rotation of the slide rotor. Eight different rinse tubes  542  corresponding to each rinse bottle  540  and each controlled by a separate pinch valve. Eight holes are provided in the slide cover  532  underneath the ends of the rinse tubes  542  so that the rinse can reach the slides.  
         [0047]    Returning to FIG. 5, also provided on the vertical wall  544  of the station housing is an extendable vacuum hose  544 . As more completely shown in cross section in FIG. 11A, the vacuum hose  544  is supported by a hose transport mechanism  570  that allows the vacuum hose  544  to be extended down into a cavity of a slide frame  510  to remove any rinse and reagent covering the tissue sample of the slide. Specifically, the suction is created by a partial vacuum generated in vacuum bottle  572  by a compressor, not shown. Consequently, the rinse and reagent is sucked in through the vacuum hose  544  and into the vacuum bottle when the vacuum hose transport mechanism  570  brings the vacuum hose end in contact with the rinse and/or reagent in cavity of the slide frame  510 .  
         [0048]    The vacuum hose transport mechanism comprises a motor  574 . A reciprocating link  576  is attached to a crank arm  575  so that the rotation of the motor  574  causes the reciprocating link  576  to traverse in a vertical direction. A bottom portion of the reciprocating link  576  is connected to a lever  578  that is pivotally attached to the station frame. The other end of this lever is connected to a vacuum hose clamp  580  that is connected via to pivot arms  582  to a plate  584  rigidly attached to the station frame. The net effect of these connections is that when the motor  574  is rotated, the slide arm  576  descends in the vertical direction. Thus, the lever  578  is pivoted clockwise around its fulcrum causing the hose clamp  580  to pivot up and away on the two pivot arms  582  from the slide as shown in FIG. 11 b . The motor is automatically turned off as the slide reaches its two extreme ends of movement by the contact of the electrical terminals  584  of the slide to the contact plates  586  connected to the station frame.  
         [0049]    A microprocessor, not shown, controls the entire dispensing assembly  500 . That is, an operator programs the microprocessor with the information such as the location of reagents on the reagent rotor and the location of slides on the slide rotor. The operator then programs the particular histochemical protocol to be performed on the tissue samples. Variables in these protocols can include the particular reagent used on the tissue sample, the time that the tissue sample is allowed to react with the reagent, whether the tissue sample is then heated to exposed or develop the tissue sample, the rinse that is then used to deactivate the reagent, followed by the subsequent removal of the rinse and reagent to allow subsequent exposure to a possibly different reagent. The dispensing assembly enables complete random access, i.e. any reagent to any slide in any sequence.  
         [0050]    An important aspect of the above-described invention is its ability to retain the fluid until such time as the solenoid hammer  10  presses on the metering chamber tubing  2 . As will be noted from FIG. 1, both one-way valves  3  and  4  are aligned in the same direction, allowing only downward flow. It was found during construction that using valves with a low opening (“cracking”) pressure resulted in the liquid dripping out of the nozzle. There are two solutions to this problem. The most obvious is to use valves with an opening pressure greater than the pressure head of liquid. In this manner, the outlet valve  4  will not allow fluid exit until a certain minimum force is applied which is greater than the pressure head of the standing liquid.  
         [0051]    A second alternative to prevent spontaneous dripping of the liquid out of the outlet valve  4  is to use a plunger  6  with an amount of friction against the inner surface of the reservoir  1  greater than the gravity pressure of the liquid  12 . An additional advantage of the plunger  6  is that it prevents spillage of the liquid  12  from the top of the reservoir  1  (which would likely occur if the reservoir were left open from above). In this manner, the plunger will not be drawn downwards inside the reservoir merely by the weight of the liquid. However, when the metering chamber is emptied and a small amount of liquid is drawn from the reservoir  1  to refill the metering chamber, the plunger&#39;s friction to the reservoir wall is overcome. The plunger  6  thereby moves downward a distance proportional to the volume of liquid expelled. We have found it useful to apply a thin coat of a lubricant such as petroleum jelly to ensure that the plunger  6  moves smoothly downward within the reservoir.  
         [0052]    Any combination of valve opening pressure and plunger friction may be used to prevent dripping, but given the low opening pressure typically found in valves of the type used, friction greater than gravity pressure of the liquid is preferred.  
         [0053]    [0053]FIG. 12 shows another alternative construction of the cartridge top. Instead of using a plunger, a one-way valve  17  is placed at the top of the reservoir  1 . The valve  17  has an opening pressure greater than the gravity pressure of the liquid within the reservoir. This third valve  17  is aligned in the same direction as the metering chamber valves  3  and  4 . This allows the entrance of air into the reservoir as liquid is removed. In this case, cracking pressure of any or all of the three valves  3 ,  4  and  17  prevents spontaneous dripping from the outlet valve. Additionally, the valve  17  prevents spillage of the contents of the reservoir.  
         [0054]    [0054]FIG. 13 shows another alternative construction for the top of the cartridge. A rolling diaphragm cover  18  is mounted at the top of the reservoir  1  and is drawn into the reservoir as the liquid is used up. This construction prevents spillage of the liquid  12  as well as provides a seal to prevent air entry. The rolling diaphragm can be made of any thin flexible elastomer such as natural rubber. The top of the rolling diaphragm can be sealed to the reservoir wall  1  by stretching the diaphragm over the reservoir, with an adhesive or by heat sealing.  
         [0055]    [0055]FIG. 14 demonstrates a third alternative construction. The top of the reservoir is closed, except for a small aperture  19  for the entrance of air. The diameter of the aperture at the top of the reservoir can be sufficiently small to effectively prevent accidental spillage of the liquid contents of the cartridge but still allow air entry as liquid is dispensed from the cartridge.  
         [0056]    A fluid level sensor may be provided adjacent to the cartridge reservoir. For example, a shaft can be connected to the top of the plunger. The shaft can be designed with a shape such that as it is drawn into the cartridge reservoir, it can optically or electrically open or close a circuit at a certain depth within the cartridge reservoir. In this manner, the shaft connected to the plunger can signal to a computer the depth of entry into the cartridge reservoir. The depth of entry would therefore be directly proportional to the amount of liquid remaining in the cartridge reservoir. Such an arrangement provides an automatic means for sensing the amount of liquid remaining inside the reservoir.  
         [0057]    A variety of different configurations for the dispensing actuators DA may be used to apply pressure on the metering chamber tubing. Although a push-type of actuator DA is shown in FIG. 1, a rotary or pull-type could also be used with slight modifications to the design, as would be obvious so as to apply a pressure on the metering chamber tubing. Additionally, a solenoid valve could also be used to control pressure to a pneumatic cylinder whose piston rod is the actuator. Alternatively, a piezoelectric transducer may apply the pressure to the metering chamber tubing.  
         [0058]    An alternative dispensing pump cartridge is illustrated in FIGS. 15 through 18. As in prior embodiments, the pump cartridge includes a liquid reservoir, in this case a flexible plastic bag  612  within a rigid housing  614 . FIGS. 15 and 16 show the housing and longitudinal section in views from the front and side. FIG. 16 shows the bag collapsed, it being recognized that it would expand to fill the volume within the housing when filled with liquid. The open end of the reservoir bag  612  fits snugly about an inlet end of a metering chamber tube  616  and is clamped and thus sealed to the tube by a plate  618  which also serves as a closure to the housing  614 . As in prior embodiments, the tube  616  is adapted to be compressed by an actuator  10  to expel liquid through a one-way outlet valve  620 . When the actuator  10  is then released, the wall of the tube  616  returns to its native position and thus creates negative pressure within the metering chamber. That negative pressure draws liquid from the liquid reservoir  612  through a one-way inlet valve  622  into the metering chamber. Significantly, both valves are passive check valves, the dispensing being controlled by the single actuator  10 . Mechanical complexity is avoided, and a cartridge may be readily replaced by dropping the cartridge into place with the tubing of the metering chamber positioned adjacent to the actuator  10 .  
         [0059]    The novel valves of this embodiment provide relatively large sealing forces to minimize leakage while still requiring very small pressure differential to open. Further, the flow path below the sealing surface of the outlet valve  620  is minimal, thus minimizing any caking of reagent on flow surfaces. As in the embodiment of FIG. 1, the one-way valves are formed from flexible leaflets. However, in this embodiment a leaflet takes the form of a flat membrane having a central pinhole which seals against a pointed protrusion. Specifically, in the outlet valve  68 , a membrane  624  is preferably formed of unitary plastic with the tube  616 . A disk  626  (FIG. 18) snaps between the membrane  624  and a molded flange  628  within the metering chamber tube  616  (FIG. 17). A valve needle  630  extends as a protrusion from the plate  626 . The needle may be a separate piece press fit into the plate  626  as illustrated in FIG. 18, or it may be molded as a unitary piece with the plate  626 . The tip of the valve needle  630  extends into the pinhole  632  within the membrane  624 , thus flexing the membrane in an outward direction. Due to the resiliency of the membrane, it presses back against the valve needle  630  with a sealing force sufficient to withstand the pressure head of the liquid contained within the metering chamber tube  616 .  
         [0060]    The plate  626  has a hole  634  to allow fluid flow therethrough. When the tube  616  is compressed by the actuator  10 , the increased pressure within the metering chamber is applied across the entire upper surface area of the membrane  624  such that a low level of pressure is required to cause the membrane to flex and break the seal about the valve needle  630 . Liquid then flows through the hole  634  and the pinhole  632 .  
         [0061]    The inlet valve  622  is similarly constructed with a membrane  636  and valve needle plate  638  retained within the internal flanges  640  and  642  in the metering chamber tube  616 . With the low pressure differential required to open the valve, the tube  616  is able to return to its native position and draw liquid into the metering chamber from the reservoir  612 . On the other hand, when the actuator  10  compresses the metering chamber  616 , the force against the membrane  636  is sufficient to seal that membrane against the valve needle of the plate  638 .  
         [0062]    A more recent embodiment of the invention was presented in U.S. patent application Ser. No. 09/032,676, entitled, “Random Access Slide Stainer With Independent Slide Heating Regulation,” filed Feb. 27, 1998, now U.S. Pat. No. 6,183,693, which is incorporated by reference in its entirety. FIGS. 19-21 present an embodiment from that patent in which independent temperature control is provided to heated surfaces, each of which supports one slide.  
         [0063]    [0063]FIGS. 19A and 19B also show the physical location of a heating element  78 , represented as a resistive element inside a rectangular box with cross-hatched lines. Each slide rests directly on the heating element  78 , so that heat is directly communicated to the microscope slide. A thermistor is incorporated into each heating element (not shown in FIGS. 19A and 19B). Each of forty-nine microscope slides  75  has its own heating element  78 , so that the temperature of each slide  75  can be independently regulated. Power for the heating element  78  is supplied directly from a temperature control board  79  that is affixed to the underside of the slide rotor  77 . Seven identical temperature control boards  79  are so mounted underneath the slide rotor  77 , evenly spaced around the periphery. Each temperature control board supplies power for seven heating elements  78 . The means by which this is accomplished is explained in reference to FIGS. 20 and 21.  
         [0064]    [0064]FIG. 20 shows the relationship between each of the heating elements  78  mounted on the slide rotor  77 , depicting the heating element  78  as a resistive element. A single sensor  87  is adjacent to each heater. The combination of a single heating element  78  and sensor  87  are so positioned so as to provide a location  88  for a single slide to be heated. The physical layout of this location  88  is demonstrated in FIGS. 19A and 19B. Two wire leads from each heating element  78 , and two wire leads from each sensor  87  are connected directly to a temperature control board mounted on the slide rotor  77 . Each temperature control board is capable of connecting to up to eight different heater and sensor pairs. Since this embodiment incorporates forty-nine slide positions, seven boards  79  are mounted to the underside of the slide rotor, each connecting to seven heater-sensor pairs. One heater-sensor position per temperature controller board  79  is not used. Also shown in FIG. 20 is the serial connection  89  of each of the seven temperature control boards, in a daisy-chain configuration, by six wires. The first temperature control board is connected via a service loop  90  to the computer  86 . The service loop contains only six wires tied together in a harness.  
         [0065]    [0065]FIG. 21 is an electronic schematic diagram of the temperature control board  79 . The design of the temperature control board  79  was driven by the need to minimize the number of wires in the flexible cable (service loop  90 ) between the heaters and the computer. To minimize the length of wires, seven temperature controller boards  79  are used, each mounted on the slide rotor. Thus, each heater is positioned close to its associated electronics and the size of each board  79  is kept small because each runs only seven heating elements  78 . Each temperature controller board  79  includes the function of an encoder and decoder of temperature data. That data relates to the actual and desired temperature of each of heating elements  78 . The data flows back and forth between the computer  86  and the temperature control board  79 . If an individual heating element  79  requires more or less heat, the computer communicates that information to the temperature control board  79 . The temperature control board  79 , in turn, directly regulates the amount of power flowing to each heater. By placing some of the logic circuitry on the slide rotor, in the form of the temperature control boards  79 , the number of wires in the service loop  90  , and their length, are minimized.  
         [0066]    In this embodiment, the temperature control board  79  system was designed as a shift register. The machine&#39;s controlling microprocessor places bits of data one at a time on a transmission line, and toggles a clock line for each bit. This causes data to be sent through two shift register chips on each control board, each taking eight bits. There are thus 16×7 or 112 bits to be sent out. Referring to FIG. 21, the data comes in on connector J 9 . 1 , and the clock line is J 9 . 2 . The shift registers used in this design are “double buffered,” which means that the output data will not change until there is a transition on a second clock (R clock), which comes in on pin J 9 . 3 . The two clocks are sent to all seven boards in parallel, while the data passes through the shift register chips (U 1  and U 2 ) on each board and is sent on from the second shift register&#39;s “serial out” pin SDOUT to the input pin of the next board in daisy chain fashion. It will be seen that a matching connector, J 10 , is wired in parallel with J 9  with the exception of pin  1 . J 10  is the “output” connector, which attaches via a short cable to J 9  of the next board in line, for a total of seven boards. The other three pins of J 9  are used for power to run the electronics (J 9 . 4 ), electronic ground (J 9 . 5 ), and a common return line (J 9 . 6 ) for temperature measurement function from the sensors.  
         [0067]    Of the sixteen data bits sent to each board, eight control the on/off status of up to eight heating elements  78  directly. This can be accomplished with a single chip because shift register U 2  has internal power transistors driving its output pins, each capable of controlling high power loads directly. Four of the remaining eight bits are unused. The other four bits are used to select one thermistor  87  out of the machine&#39;s total complement of forty-nine. For reasons of economy and to reduce the amount of wiring, the instrument has only one analog-to-digital converter for reading the forty-nine temperature transducers (thermistors  87 ), and only one wire carrying data to that converter. This channel must therefore be shared between all of the transducers (thermistors  87 ), with the output of one of them being selected at a time. Component U 4  is an analog multiplexer which performs this function. Of the four digital bits which are received serially, one is used to enable U 4 , and the other three are used to select one of the component&#39;s eight channels (of which only seven are used). If pin four is driven low, U 4  for that board  79  becomes active and places the voltage from one of the seven channels of that board on the shared output line at J 9 . 6 . Conversely, if pin four is pulled high, U 4 &#39;s output remains in a high impedance state and the output line is not driven. This allows data from a selected board  79  to be read, with the remaining boards  79  having no effect on the signal. Multiplexer U 4  can only be enabled on one board  79  at a time; if more than one were turned on at a time, the signals would conflict and no useful data would be transmitted.  
         [0068]    Temperature sensing is accomplished by a voltage divider technique. A thermistor  87  and a fixed resistor (5.6 kilohms, R 1 -R 8 , contained in RS 1 ) are placed in series across the 5 volt electronic power supply. When the thermistor is heated, its resistance drops and the voltage at the junction point with the 5.6 kilohm resistor will drop.  
         [0069]    There are several advantages to the design used in this embodiment. Namely, the temperature control boards  79  are small and inexpensive. Moreover, the heater boards are all identical. No “address” needs to be set for each board  79 . Lastly, the service loop  90  is small in size.  
         [0070]    An alternative potential design is that each temperature control board  79  could be set up with a permanent “address” formed by adding jumper wires or traces cut on the board. The processor would send out a packet of data which would contain an address segment and a data segment, and the data would be loaded to the board whose address matched the address sent out. This approach takes less time to send data to a particular board, but the address comparison takes extra hardware. It also demands extra service loop wires to carry the data (if sent in parallel) or an extra shift register chip if the address is sent serially. As yet another potential design is that each temperature control board  79  could have its own microprocessor. They could all be connected via a serial data link to the main computer  86 . This approach uses even fewer connecting wires than the present embodiment, but the cost of hardware is high. It also still implies an addressing scheme, meaning that the boards would not be identical. Also, code for the microprocessors would be required.  
         [0071]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, the pump is operable with the metering chamber positioned above the reservoir. Disclosure Document No. 252981 filed May 10, 1990 at the U.S. Patent and Trademark Office shows details of a potential system embodying the present invention.