Patent Publication Number: US-2009228035-A1

Title: Lancet Assembly

Description:
TECHNICAL FIELD 
     The present invention relates to a lancet assembly constituted from a lancet and a lancet case that houses the former, an injector used in combination with the lancet assembly, and a pricking device constituted from the lancet assembly and the injector. Such device is used in pricking a predetermined portion of a body with a sharp pricking member such as a needle for sampling an amount of body fluid such as blood. 
     BACKGROUND ART 
     Various pricking devices have been used to take a small amount of blood for the purpose of measuring the blood sugar level of patients with diabetes. Such a device is constituted from a lancet having a pricking member that pricks a predetermined portion of the body of a patient and an injector. The lancet is incorporated in the injector that launches the lancet with the pricking member exposed at the distal end thereof, the lancet being launched toward the predetermined portion by making use of the expanding action of a compressed spring provided in the injector. 
     When taking an amount of blood by using such a pricking device as described above, particular attention must be paid in the handling of the lancet that has been used. In the lancet that has been used, typically the distal end portion of the pricking member that bears a trace of the patient&#39;s blood is exposed from a lancet body. Should a portion of the body of a person other than the patient, for example a nurse who takes the blood sample, accidentally touches the distal end portion of the pricking member, the body portion may be pricked by the distal end portion of the pricking member causing a cut through which the patient&#39;s blood may enter the other person&#39;s body, thus posing the danger of infection of a disease. 
     Known pricking devices are not necessarily designed with due consideration given to the handling of the lancet that has been used. For example, it has been proposed to apply a cap on the exposed distal end portion of the pricking member after the pricking operation (refer to Patent Document 1 which will be mentioned later). This device requires the lancet to be handled in the state of its distal end thereof exposed so as to apply the cap thereon, and therefore the danger described above is not eliminated. 
     Accordingly, the pricking device requires utmost attention in handling the lancet after it has been used, and there is a demand for a pricking device that allows the lancet to be handled after safety thereof has been ensured. 
     Patent Document 1: U.S. Pat. No. 5,385,571 
     DISCLOSURE OF THE INVENTION 
     Problem to Be Solved by the Invention 
     It is an object of the present invention to provide a pricking device that allows a lancet to be removed from an injector after isolating a protruding distal end portion of a pricking member from its surrounding, rather than removing the lancet from the injector with the distal end portion of the pricking member remaining in the state of protruding from a lancet body, after pricking. 
     Means to Solve the Problem 
     In the first embodiment, the present invention provides a lancet assembly comprising a lancet and a lancet case that houses a portion of the former, wherein 
     the lancet comprises a lancet body, a lancet cap and a pricking member, 
     the lancet is a molded article with the pricking member inserted in which the pricking member is disposed in the lancet body and the lancet cap while straddling over these members, and the distal end portion of the pricking member is enclosed by the lancet cap, and the lancet cap and the lancet body are connected together via a weakened portion; 
     the lancet body comprises a protruding portion, 
     the lancet case comprises a case body and a pair of wings disposed on both sides of the case body; and 
     each wing has a stopper that protrudes inward between its front end portion and its rear end portion, the front end portion is connected to the case body and the rear end portion is left free and, as a result, when the stopper receives a force acting outward, the wing is elastically able to splay outward. It is noted that the force acting outward is applied to or in the vicinity of the rear end portion of the wing usually by a wing splaying member as described later when the lancet assembly and an injector according to the present invention. As will be seen clearly from the below detailed description with drawings referred to, the wings extend along the side surfaces of the lancet case or form portions of the side surfaces of the lancet case when no force is applied. 
     With such lancet assembly according to the present invention, when the lancet is inserted in the lancet case such that the weakened portion is located in the lancet case and the protruding portion of the lancet body is positioned between the stopper of the wing and the rear end opening of the case body, 
     (a) a portion (a rear portion) of the lancet cap and a portion (particularly a front portion) of the lancet body are housed (therefore, a portion of the lancet is housed) in the lancet case, 
     (b) when no force is applied to the wing of the lancet case, the protruding portion of the lancet body is able to move back and force between the stopper of the wing and the rear end opening of the lancet case, but due to abutment against the stopper, the protruding portion of the lancet body is unable to move ahead over the stopper, and due to abutment against an inner wall of the rear end opening or abutment against a protruding portion which protrudes inward at the rear end opening, the protruding portion of the lancet body is unable to move rearward over the rear end opening. 
     It is noted that when the force acting outward is applied to the stopper of the wing, the wing elastically splays outward while the front end portion of the wing is connected to the case body. As a result, the protruding portion of the lancet body does not abut against the stopper as described above, and therefore the protruding portion becomes able to move forward. 
     The lancet assembly of the present invention surely keeps the state wherein the wings are elastically splayed outward as described above by using an injector into which the lancet assembly is incorporated, and then the pricking operation as to a predetermined portion is carried out by launching a lancet body with a distal end portion of the pricking member exposed so as to move the protruding portion of the lancet body moves forward ahead of the stopper. 
     After the pricking operation, by removing the force applied to the elastically splayed out wing so as to return the wing toward its original form, the protruding portion of the lancet body again becomes able to move only between the stopper and the rear end opening of the case body by means of the action of the stopper and the protruding portion of the lancet body. By designing the case body such that the exposed distal end portion of the pricking member is located sufficiently away back from the front end opening of the case body, no accidental contact with the distal end portion of the pricking member from the front end opening of the case body is substantially eliminated after the pricking operation with the lancet assembly, the lancet assembly used for the pricking operation can be disposed safely. 
     It is noted that the removal of the force as described above is carried out automatically when the lancet assembly which was used for the pricking operation is ejected from the injector, so that the risk as to the distal end portion of the pricking member is substantially eliminated with thus ejected lancet assembly. 
     AS to the lancet assembly according to the present invention, the lancet case described above is preferably constituted by integrally forming the case body and the wings by molding (particularly injection molding) from a resin such as a polypropylene resin, a polyethylene resin, a polystyrene resin, a POM resin (polyacetal resin), a nylon resin, an ABS resin, a polycarbonate resin, a vinyl chloride resin, an elastomer resin, a silicone resin, a rubber based resin, a PBT resin (polybutylene terephthalate resin), a polyester copolymer resin or the like. As for the lancet, the pricking member is usually made of a metal, for example, a stainless steel, and the other portion may be formed of a resin similar to that of the lancet case, and is preferably formed by the injection molding with the pricking member being inserted. 
     In the lancet assembly according to the present invention, the breakage of the weakened portion of the lancet can be carried out by turning (so-called twisting) the lancet cap and the lancet body along relatively opposite directions around the extending direction of the pricking member. That is, the weakened portion is designated such that the above mentioned turning is sufficient for breaking the weakened portion. For example, a resin material for forming the lancet and/or a thickness of the weakened portion is appropriately selected. After breaking the weakened portion as described above, the distal end portion of the pricking member is exposed. 
     In order to facilitate the breakage of the weakened portion by turning the lancet cap and the lancet body along the relatively opposite directions, the lancet body and the lancet case are designated such that the lancet body does not turn in-the lancet case relatively around the extending direction of the pricking member. Specifically, the lancet body and the lancet cap are adopted such that a portion of an inside wall which defines an inner space of the case body is present inside a trajectory of the lancet body which is formed by rotating the lancet body around the extending direction of the pricking member. In this case, it is preferable that the lancet body is not of an axial symmetry shape with respect to extending direction of the pricking member 
     In contrast, the lancet body and the lancet cap are preferably designed such that a portion of the lancet cap which is positioned near the lancet cap, namely the rear portion of the lancet cap is able to rotate in the lancet case around the extending direction of the pricking member. Specifically, the lancet body and the lancet cap are such that an inside wall which defines the inner space of the case body is located outside a trajectory of the lancet cap (its rear portion) which is formed by rotating the lancet cap around the extending direction of the pricking member. In this case, it is preferable that the lancet body is of an axial symmetry shape with respect to extending direction of the pricking member (for example, a column form). 
     As to the inner space of the case body, its cross section perpendicular to the extending direction of the pricking member does preferably not change so much, and it is more preferable that such cross section does substantially not change. For example, the shape of the cross section of the inner space of the case body is made rectangular. In this case, for example, the shape of the cross section of the lancet body has other shape which makes it impossible to rotate in said rectangular shape of the case body (for example other rectangle or a square, a oval or the like) while the rear portion of the lancet cap has a circular cross section which makes it possible to rotate in said rectangular shape. 
     The lancet comprising the lancet body, the lancet cap and the weakened portion provided therebetween is preferably manufactured by molding a resin with the pricking member being inserted therein (so-called insert molding process) as mentioned previously. This method is advantageous in that it is possible to easily manufacture the lancet in large numbers that comprises the lancet body and the lancet cap that are integrally connected via the weakened portion while the pricking member extends in these members straddling therebetween. The weakened portion is preferably formed by making the thickness smaller in the portion of the resin layer that surrounds the pricking member, for example by forming a notch therein. In other preferable embodiment, the weakened portion can be formed by forming an incision in the resin layer that does not reach the pricking member after forming the resin layer that surrounds the pricking member. 
     In one preferred embodiment, the lancet cap has a protruding portion that protrudes outward, which protruding portion preferably extends over substantially the entire circumference of the lancet cap. The protruding portion has an external profile larger than an inner profile of the front end opening of the lancet case, so that the protruding portion cannot enter the inner space of the lancet case through the front end opening since the protruding portion abuts against the front end of the is lancet case so that no further movement of the lancet rearward relative to the lancet case is prevented when the lancet is inserted in the lancet case so as to form the lancet assembly. 
     In one preferred embodiment, the stopper of the wing has a tapered shape which extends inward with respect to the rearward direction of the lancet case. In this embodiment, when the lancet body is inserted in lancet case through its front end opening and moved rearward relative to the lancet case so as to make the protruding portion of the lancet body abut against the stopper and then lancet body is intentionally moved further back by applying a rearward force to the lancet, the protruding portion presses a surface of the tapered shape outward, so that the wing elastically splays out, and then returns to its original shape after it has passed over the tapered shape. 
     In one preferred embodiment, the lancet case comprises a front end opening and a rear end opening stopper of the wing, and when the lancet body is inserted in the lancet case through the front end opening and moved therein rearward, the protruding portion of the lancet body abuts against a wall which defines the rear end opening of the lancet case. In this embodiment, the profile of the protruding portion of the lancet body is larger than an inner profile of the rear end opening of the lancet case. As a result, a further rearward movement of the lancet body in the lancet case becomes substantially impossible. That is, the lancet does not get out of the rear end opening of the lancet case. 
     In one preferred embodiment, the lancet case comprises a protrusion behind the front end portion. The protrusion fits in a recess which is provided inside and behind an front end opening of the injector, so that lancet assembly is loaded in the injector. In other embodiment, the lancet case comprises a recess and the injector comprises a protrusion behind the front end opening of the injector, which protrusion fits in the recess of the lancet case. In other words, one of two members which get in the fitting or engaging relationship with each other is present behind the front end portion while the other member is located inside and behind the front end opening of the injector. With such engaging or fitting members, the lancet is mounted on the injector in place by fitting in fitting in with each other, for example by snap fitting when the lancet assembly is inserted in the injector. 
     In the present invention, the lancet case is preferably formed by molding of a resin, particularly injection molding of a resin. When such molding is used, the lancet case is readily prepared wherein the front end portion of the wing is connected to the case body together, and also the nature of the wing to elastically spay out is readily ensured. 
     In the present invention, the lancet body of the lancet comprises a rear end portion which fits in a front end portion of a plunger of the injector according to the present invention which will be explained below. The plunger launches the lancet. Such rear end portion comprises a protrusion or a recess around its outside, and such protrusion or the recess fits in a recess or a protrusion which is provided on the front end portion of the plunger complementarily to the former protrusion or the recess. As to the relationship of such protrusion and the recess, the above mentioned relationship between said “two members which get in the fitting or engaging relationship with each other” is similarly applicable. 
     With such members, namely the protrusion and the recess, when the lancet assembly is inserted in the injector through its front end opening, and the rear end portion of the lancet body is moved rearward so as to abut against the front end portion of the plunger, and further moved rearward, the rear end portion of the lancet body is such that it fits in the front end portion of the plunger. 
     In the second aspect, the present invention provides the injector which is used in combination with the lancet assembly described above and also below so as to launch the lancet body with a distal end portion of the pricking member exposed, 
     which injector comprises a member which splays (or expands) outward each wing (corresponding to the wing splaying member described above) therein, and 
     when the lancet assembly is inserted rearward in the injector through its front end portion, each wing of the lancet case is such that it elastically splays out by means of said member which splays outward the wing. 
     The member which splays out each wing elastically splays out or expands the wing while the front end portion of the wing is in the condition in which it is connected to the case body, so that the wing extends rearward obliquely from the case body. 
     In one embodiment, the wing splaying member is a pair of wedge-shaped member which are located within the injector, 
     each wedge-shaped member has a tapered off shape (toward its front) while separated from the other wedge-shaped member so that it defines a slope which is inclined (inward) toward the front of the injector, and 
     when the lancet assembly is inserted rearward in the injector through its front end opening, the rear end portion of each wing of the lancet case is located so as to mount on the front end portion of the slope of the wedge-shaped member, and then when such insertion is further continued, the rear end portion of the wing slides on the slope, so that the wing elastically splays outward. The provision of such wedge-shaped members as described above makes it possible to automatically splay out the wings only by inserting the lancet assembly, which is convenient. 
     In the state wherein the wings are in the splaying out condition, the forward movement of the lancet body cannot be prevented by the abutment of the protruding portions of the lancet body against the stoppers of the wings when the lancet body moves along the pricking direction. 
     In one embodiment, it is preferable that the injector further comprises an ejector that is capable of applying a force acting forward on the lancet case that has been inserted. By moving such an ejector forward, a force can be applied to the rear end portion of the lancet case in the state where for example a bump disposed behind the front portion of the lancet case is fitting in for example an recess at the front end opening of the injector. 
     When the force is applied to the rear end portion of the lancet case, the bump as fitting in the recess comes out of the recess, so that the lancet case is moved forward. As a result, the force which has been applied to the wings by the members which splay out the wing is removed, so that the wings return to their original forms. Then, the ejector is further moved forward, so that the lancet assembly loaded in the injector is dischargede from the injector. 
     In one embodiment, the member which is able to apply a forward force to the loaded lancet case abuts against the rear end portion of the lancet case when the loading of the lancet assembly in the injector has been completed or when the ejector is moved forward. 
     Particularly, it is preferable that a member which is able to apply a forward force to the rear end portion of the inserted lancet case, preferably a rear end portion of a side of the lancet case on which side no wing is present. For example, the ejector abuts against the rear end portion of a side surface of the lancet case which surface is adjacent to the side surface on which the wing is present. 
     In one embodiment, the plunger comprises a spring between a protrusion provided around an intermediate portion of the plunger and a rear partition provided in the injector housing, 
     upon loading of the lancet assembly into the injector, the rear end of the lancet abuts against the front end of the plunger, which is moved rearward so that the spring is compressed by such plunger, and the protrusion of the plunger moves a rear end of a trigger lever (or a shoulder at a rear portion of the trigger lever in the embodiment in the drawing which is referred to below) outward to which a inward force is applied, and then when the protrusion is further moved rearward beyond the rear end (or the shoulder) of the trigger lever, the rear end of the trigger lever is returned inward, so that the protrusion (in the form of for example a flange) is engaged with the rear end of the trigger lever while the spring is kept in the compressed condition, 
     after such engagement, a rearward force is applied to the rear end of the lancet body due to the plunger being impossible to move back, so that the rear end portion of the lancet body is grasped by the plunger. In other embodiment, the above described engagement may be caused after the rear end portion of the lancet body is grasped by the plunger. 
     After such engagement is achieved, when the engagement is removed by moving the rear end (or the shoulder) of the trigger lever outward, the spring in the compressed condition expands at once. Such expansion is used for launching the lancet body which is in the free condition as described above while the distal end portion of the pricking member is exposed so as to prick a predetermined portion. 
     In one embodiment, the injector according to the present invention comprises 
     a pricking depth adjusting drum disposed behind and adjacent to the rear partition in the injector housing, 
     the rear end portion of the plunger extends through the drum, 
     the drum has a ring-shaped member on the inside at the front end of the drum which member is capable of rotating around the plunger, 
     the length of the ring-shaped member in the pricking direction changes along the circumferential direction thereof continuously or stepwise, 
     the rear end of plunger has a hitting member that strikes the rear end surface in a portion along the circumferential direction of the ring-shaped member, 
     when the plunger moves forward for pricking, the hitting member on the rear end of plunger strikes a portion of the rear end surface of the ring-shaped member in the drum, and is therefore unable to move further forward, 
     a portion of the rear end surface of the ring-shaped member as an object which the hitting member provided on the rear end of the plunger strikes can be changed by causing the ring-shaped member to rotate around the plunger by means of the drum rotation, so that the length between the rear partition of the housing of the injector and the rear end of the plunger is changed upon striking of the hitting member. Therefore, when the hitting member on the rear end of the plunger strikes a portion of the rear end surface of the ring-shaped member in the drum, the length of a plunger portion which is located ahead of the rear partition is changed, that is the pricking depth is changed. 
     Since the length of the plunger itself (the entire length) is fixed, the length of the distal end portion of the pricking member which protrudes out of the front end opening of the lancet case can be changed upon pricking by being able to change the distance from the rear partition up to the rear end of the plunger. 
     It is noted that the present invention provides the lancet that constitutes the lancet assembly of the present invention described above, the lancet case that constitutes the lancet assembly of the present invention described above, the kit of the lancet and the lancet case for constituting the lancet assembly of the present invention described above, the pricking device composed of the lancet assembly of the present invention described above and the injector of the present invention described above, and the kit of the pricking device constituted from the lancet assembly of the present invention described above and the injector of the present invention described above. 
     Effects of the Invention 
     In the case wherein the lancet assembly of the present invention and the injector of the present invention are combined and used as the pricking device of the present invention, preparation for the pricking operation is completed only by merely inserting the lancet assembly so as to load it into the injector and twisting off the lancet cap. The pricking device also allows it, after the pricking operation, to remove the distal end portion of the pricking member from the injector in a state of being substantially isolated in the lancet case from the surrounding, although it is still protruding from the lancet body. It is noted that “the state of being substantially isolated from the surrounding” means that the distal end portion of the pricking member is located at a position sufficiently away from the front end opening of the lancet case, and therefore a person who takes the blood sample does not normally touch the distal end portion in the routine pricking operations. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view of a lancet assembly of the present invention. 
         FIG. 2  is a schematic perspective view of a lancet assembly of the present invention, with a near side half of the lancet case being cut away (wings are closed) for the ease of understanding the structure. 
         FIG. 3  is a schematic perspective view of a lancet assembly of the present invention with its near side half being cut away. 
         FIG. 4  is a schematic perspective view of an injector into which the lancet assembly is loaded. 
         FIG. 5  is a schematic perspective view of the injector with the lancet assembly being loaded therein. 
         FIG. 6  is a schematic perspective view of a lancet that constitutes the lancet assembly of the present invention. 
         FIG. 7  is a schematic perspective view of the state of the lancet assembly being inserted with a near side housing half of the injector housing being removed. 
         FIG. 8  is a schematic perspective view of the state of the lancet assembly being inserted (the same state as in  FIG. 7 ) with a near side half of the lancet case being cut away. 
         FIG. 9  is a schematic perspective view of the state in which the lancet assembly has just been loaded in the injector similarly to  FIG. 7 . 
         FIG. 10  is a schematic perspective view of the state in which the lancet assembly has just been loaded in the injector similarly to  FIG. 8 . 
         FIG. 11  is a schematic perspective view of the state in which the lancet cap has been removed from the state shown in  FIG. 9 , similarly to  FIG. 7 . 
         FIG. 12  is a schematic perspective view of the state in which the lancet cap has been removed from the state shown in  FIG. 10 , similarly to  FIG. 8 . 
         FIG. 13  is a schematic perspective view of the state in which the distal end portion of the pricking member has just protruded from the front end opening of the lancet case, similarly to  FIG. 7 . 
         FIG. 14  is a schematic perspective view of the state in which the distal end portion of the pricking member has just protruded from the front end opening of the lancet case, similarly to  FIG. 8 . 
         FIG. 15  is a schematic perspective view of the state in which the lancet body is removed rearward from the state shown in  FIG. 13 , similarly to  FIG. 7 . 
         FIG. 16  is a schematic perspective view of the state in which the lancet body is removed rearward from the state shown in  FIG. 14 , similarly to  FIG. 8 . 
         FIG. 17  is a schematic perspective view of the state in which the lancet case is being moved forward by means of an ejector, similarly to  FIG. 7 . 
         FIG. 18  is a schematic perspective view of the state in which the lancet case is being moved forward by means of an ejector, similarly to  FIG. 8 . 
         FIG. 19  is a schematic perspective view of the plunger. 
         FIG. 20  is a schematic perspective view of the state of a housing half that constitutes the injector housing. 
         FIG. 21  is a schematic perspective view showing the lancet assembly in the state where the wings are splayed out. 
         FIG. 22  is a schematic perspective view of the ejector. 
         FIG. 23  is a schematic perspective view of the lancet assembly which has been discharged from the injector. 
         FIG. 24  is a schematic perspective view of a ring-shaped member and a hitting member. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       100 : Lancet assembly 
       102 : Lancet case 
       104 : Front end opening 
       106 : Front end opening 
       107 : Rear end opening 
       108 : Rear end portion 
       110 : Front end portion 
       112 : Bump 
       114 : Case body 
       116 : Wing 
       118 : Front end portion 
       120 : Rear end portion 
       122 : Stopper 
       124 : Sloped surface 
       126 : Rear portion surface 
       128 : Side surface 
       130 : Rear end surface 
       132 : Rear end wall 
       140 : Rail 
       200 : Lancet 
       202 : Rear end portion 
       204 : Lancet body 
       206 : Lancet cap 
       208 : Weakened portion 
       210 : Pricking member 
       212 : Protruding portion 
       218 : Bump 
       220 : Bump 
       222 : Protruding portion 
       300 : Injector 
       301 : Plate-like portion 
       302 : Front end opening 
       303 : Protrusion 
       304 : Protruding portion 
       306 ,  308 : Injector housing half 
       309 : Housing 
       310 : Plunger 
       314 : Front end portion 
       315 : Seat surface 
       316 : Recess 
       320 ,  322 : Leg 
       324 : Protruding portion 
       330 : Shoulder 
       340 : Wedge-shaped member 
       341 : Front end portion 
       342 : Slope 
       343 : Cut away defining wall 
       344 : Front partition 
       346 : Protrusion 
       348 : Recess 
       350 : Push button 
       351 : Base plate 
       354 : Operation button 
       356 : Pusher 
       358 : Rear partition 
       360 : Pricking depth adjusting drum 
       361 : Ring-shaped member 
       362 : Rear end portion of plunger 
       363 : Opening 
       365 : Hitting member 
       367 ,  367 ′: Hitting portion 
       369 : rotation limiting member 
       371 ,  371 ′,  373 ,  373 ′: Step 
     BEST MODES FOR CARRYING OUT THE INVENTION 
     The lancet assembly of the present invention, the lancet and the lancet case that constitute the same, the injector that is used in combination with the lancet assembly, and a pricking device of the present invention will be described below in detail with reference to the accompanying drawings. The moving direction of the lancet for pricking (that is, the direction of the pricking member which is moving for pricking, which is also referred to pricking direction) corresponds to a “front” meaning direction, and the opposite direction corresponds to a “rear” meaning direction, and the terms relating to the directions in the present specification are used based on such directions. 
     The lancet assembly according to the present invention is schematically shown in  FIG. 1  in a perspective view. It is noted that for the purpose of readily understanding the structure of the lancet assembly,  FIG. 2  shows the lancet assembly with a near side half of the lancet case being cut away in a schematic perspective view while  FIG. 3  shows the lancet assembly with a near side half thereof being cut away in a schematic perspective view. Those drawings show the lancet assembly in a completed form as an assembly wherein the lancet  200  is incorporated in the lancet case  102 . The lancet case  102  is in the form of for example a rectangular column as a whole, and the rear end portion  202  of the lancet  200  is inserted rearward in the inside of the lancet case through the front end opening  106  of the lancet case, and thereby the lancet assembly  100  is assembled. The lancet case  102  has an opening  106  (at the front end) and an opening  107  (at the rear end), and a predetermined portion (for example, a finger tip) is applied onto the front end opening  106  upon pricking. 
       FIG. 4  schematically shows the injector  300  into which the lancet assembly is loaded in a perspective view, and  FIG. 5  schematically shows the injector  300  with the lancet assembly being loaded in a perspective view. As described below, the injector  300  includes a mechanism which launches the lancet in a space of the housing  309 . defined by injector housing halves  306  and  308 . Loading of the lancet assembly  100  in the injector  300  is carried out by inserting, through the front end opening  302  of the lancet case toward the inside thereof, the rear end portion  108  of the lancet case first, and then the most portion of the lancet. The lancet case  102  has a bump (or protrusion)  112  which is positioned behind the front end portion  110  of the lancet case, and such bump  112  gets over the protruding portion ( 304 , see  FIG. 7 ) positioned on the injector inside behind the front end opening  302  of the injector, preferably followed by fitting in a complementary recess positioned behind the protrusion, so that the loading of the lancet assembly into the injector is completed to be in the state-as shown in  FIG. 5 . 
     The lancet  200  shown in  FIG. 6  in a perspective view which forms the lancet assembly according to the present invention comprises a lancet body and lancet cap  206 , which are connected together through a weakened portion  208 . In the lancet  200 , the pricking member  210  (see  FIG. 3 ) is disposed to extend in the lancet body  204  and the lancet cap  206  while straddling over these members, and the distal end portion of the pricking member  210  is enclosed by the lancet cap  206 . Such lancet  200  is formed by molding a resin (a resin molded product) with the pricking member  210  inserted therein. The lancet body  204  has a protruding portions  212  on the outside thereof. 
     The rear end portion  202  of the lancet body  204  is configured such that it fits in the front end portion  314  of the plunger  310  in the injector  300 . The rear end portion  202  comprises a bump  218  around its outside, and the bump is configured such that it fits in a complementary recess  316 . The relationship between the bump and the recess as described is similar to that of the above mentioned “two members which get in the fitting or engaging relationship with each other”, and thus what is applicable to the latter relationship is similarly applicable to the former relationship. It is possible to use a recess in place of the bump, and to use a bump in place of the recess. 
     he lancet body further comprises other bump  220  in front of the bump  218 . A rear surface  221  of this bump  220  is in the condition of abutment against a seat surface  215  which is provide at the front end of the plunger  310  when the loading of the lancet assembly is completed. 
     With the lancet as described, the weakened portion  208  is configured such that it is broken by applying a force which turns the lancet body  204  and the lancet cap  206  in opposite directions around the extending direction of the pricking member  210 , or in addition or in place of such force, by applying a force to make these members separate from each other along the pricking direction of the pricking member. After breaking the weakened portion, when the lancet cap  206  is brought away from the lancet body  204 , the distal end portion of the pricking member  210  is exposed from the lancet body  204 . 
     The lancet case  102  which forms the lancet assembly according to the present invention comprises a pair of the wings  116  which are located on the side surfaces, preferably the opposing side surface of the case body  114 . Such wings preferably extend along the side surfaces of the lancet case (thus, the wings substantially form portions of the side surfaces of the lancet case). Each wing  116  comprises the stopper  122  which protrudes inward between its front end portion  118  and its rear end portion  120 . The front end portion  118  is connected to the case body  114 , and the rear end portion  120  is free. As a result, when the lancet  200  is inserted in the lancet case  102  through its front end opening  106 , the protruding portions  212  of the lancet body  204  abut against the stoppers  122 , and the lancet is moved further rearward, the protruding portions  212  go up over slopes  124  of the stoppers  122 , so that outward forces are applied to the wings, and thereby the wings  116  are elastically splayed outward. 
     Thereafter, when the protruding portions  212  pass over the stoppers  122 , the wings  116  return to their original forms to be in the state as shown in  FIG. 2 . The rear surface  126  of the stopper  122  is at right angle relative to the wing  116  or at an angle close to such angle. As a result, in the state as shown in  FIG. 2 , even when a forward force is applied to the lancet, the protruding portion  212  abuts against the rear surface  126  so that the lancet is not able to move forward any further, and therefore the forward movement of the lancet is prevented. Once the protruding portion  212  has passed over the stopper  120  to be present behind the stopper, the protruding portion cannot move ahead of the stopper  120 . In the state wherein the protruding portion  212  has just passed over the stopper  120 , the rear end portions with the two bumps (or protrusions)  218  and  220  in the condition of extending rearward (namely outward) from the rear end opening  107  of the lancet case  102 . 
     The lancet cap  206  has a grip portion on its front end portion  214  which is pinched when the weakened portion  208  is broken as described above, and the lancet cap has a protruding portion  216  behind such grip portion. The protruding portion  216  is preferably in the form of a flange as shown, and it abuts against a portion which defines the front end opening  106  of the lancet case  102 , so that the lancet  200  cannot move rearward any further relative to the lancet case  102 . 
     Thus, when a forward force is applied to the lancet  200  in the state of the lancet assembly  100  as assembled as shown in  FIG. 2 , the lancet does not get out of the front end opening  106  of the lancet case  102 . Also, the lancet does not get out of the rear end opening  107  even when a rearward force is applied to the lancet  200 . 
     The lancet assembly which has been assembled as described above is inserted in the injector  300  through its front end opening  302  as shown in  FIG. 4 , so that the state shown in  FIG. 5  is achieved after the bumps  112  of the lancet passed over the protruding portions  304 , and this states corresponds to the completion of loading. 
       FIGS. 7 and 8  show, in perspective views, steps on the way to loading of the lancet assembly in the injector. For the ease of understanding the relationship between the lancet assembly  100  and the injector  300  as well as the inner structure of the injector,  FIG. 7  shows the state where the housing half located on the near side of the injector housing is removed. For the ease of understanding the pricking depth adjusting mechanism which will be described later,  FIG. 8  shows the state where the near side half of the lancet case  102  is cut away, and for the ease of understanding the state of the plunger  310  which launches the lancet, a near side half of the ejector  312  described below is cut away and also a near side half of a drum rotation limiter  380  which will be described later is removed. 
     As shown in  FIG. 19 , the front end portion  314  of the plunger  310  is bifurcated into two portions, and a first leg  320  and a second leg  322  that define a small gap  318  therebetween. The plunger is formed by, for example, molding a plastic material, so that the first leg  320  and the second leg  322  are capable of elastically deforming. When these legs are subjected to forces acting outwardly as indicated by the arrows, these legs deflect outward so as to expand the gap  318 . 
     With this configuration, when the lancet assembly  100  shown in  FIG. 1  is inserted into the injector  300  as shown in  FIG. 7 , the rear end portion  202  of the lancet body  204  approaches, after the state of  FIG. 7 , the seat surfaces  315  of the front end portion  314  of the plunger in the state as shown in  FIG. 19 , and then abuts against the surfaces  315 . An attempt of inserting the lancet assembly thereafter causes the rear end portion  202  of the lancet body  204  to apply a force of pressing backward to the seat surfaces  315 . Since the seat surfaces  315  are inclined, this force also generates a force that acts in the direction indicated by the arrows, so that the leg  320  and the leg  322  elastically splay toward the outside. 
     When the first leg  320  and the second leg  322  splay out as described above, the rear end portion  202  of the lancet body  204  can move further rearward, so that the bump  218  of the rear end portion  202  of the lancet body  204  fits into the recesses  316  and, at the same time, the legs that have expanded outward move to return somewhat so as to restore the original shape. As a result, the rear end portion  202  is held between the legs  320  and  322  and snugly fits into the gap  318 . At this time, the surface  221  that opposes to the front side of the protruding portion  218  of the lancet body makes close contact with the seat surfaces  315  provided on the distal end of the plunger  310 . 
       FIGS. 9 and 10  show the state in which the lancet assembly  100  has just been loaded in the injector  300 , similarly to  FIGS. 7 and 8 . As seen from  FIG. 10 , the rear inclined surface  221  of the bump  220  of the lancet body  204  is abutting against the seat surfaces  315  of the front end of the plunger  310 . 
     The plunger  310  has a launching spring (not shown) disposed around the plunger  310  behind the protruding portion  324  provided around an intermediate portion of the plunger (for example between protruding portion  324  and the rear partition  358 ). When the lancet assembly is loaded in the injector, the rear end portion  202  of the lancet which abuts against the front end portion  314  of the plunger moves the plunger back so as to compress the spring. Upon such compression, the protruding portion  324  of the plunger is moved backward on the lower edge of the trigger lever  328 , while exerting a force that pushes upward the trigger lever pivoted by a shaft  326  against the force exerted downward by the trigger lever  328 . 
     Then immediately after the protrusion  324  has passed below the shoulder  330  located at the rear end of the trigger lever, the shoulder  330  of the trigger lever abruptly moves downward (by means of the above mentioned downward force), so that the protruding portion is in the condition of being engaged with the shoulder  330 . In this situation, in spite of the fact that the forward force is applied to the plunger by the compressed launching spring, the state as shown in  FIG. 9  in which the protruding portion  324  is engaged with the shoulder  330  is kept even though the force which is applied to move the plunger rearward is removed. That is, the so-called cocking state is achieved for launching of the lancet. 
     In the state wherein the protruding portion  324  is engaged with the shoulder  330  located on the rear end of the trigger lever, it is preferable that the gap (or space)  318  at the front of the plunger does not expand, and therefore it is preferable that the first leg  320  and the second leg  322  of the plunger do not deform so as to splay outward. In order to prevent such expansion, it is preferable that the front partition  344  provided in the housing has a cut away portion  345 , and a wall  343  which defines the cut way portion just surrounds the front end portion  314  of the plunger  310 , so that the front end portion  314  of the plunger does not expand. 
     It is noted that in the embodiment illustrated, a plate-shaped member  301  extends toward the rear from the upper edge of the end surface of the shoulder  330  located at rear end of the trigger lever. The plate-shaped member  301  is adapted such that when a button  350  is depressed inward to launch the lancet, the plate-shaped member  301  presses the protrusion  303  in the housing and undergoes elastic deformation, so that a force is exerted by the deformation to push back the button (see  FIG. 11 ). 
     When the rear end portion of the lancet body is moved rearward so as to make it abut against the front end portion of the plunger, and then the lancet body is moved further rearward, the rear end portion of the lancet is such that it fits in the front end portion of the plunger. It is noted that such fitting of the rear end portion of the lancet body may occur after the rear end portion of the lancet body move the plunger rearward so as to make no further rearward movement impossible. In other embodiment, the fitting may occur first, and then the rearward movement of the lancet body moves the plunger rearward. 
     At the completion of the loading of the lancet assembly  100  into the injector  300  as shown in  FIGS. 9 and 10 , the attention is to be paid to that the wings  116  on the both sides of the lancet case  102  are in the condition of being splayed out. The reason why the wings are in the splayed out condition is that a pair of wedge-shaped members  340  are provided as the wing splay member in the injector. Such wedge-shaped members are separated from each other and have a tapered off form (that is, sharpened form with respect to the front direction), so that they form sloped surfaces  342  which are inclined with respect to the front of the injector. 
     The wedge-shaped members are provided in the housing half  306  which is schematically shown in  FIG. 20 . In the shown embodiment, the wedge-shaped members  340  are provided by fitting a member as a separate member in the housing half  306 . The wedge-shaped member is configured such that the front ends  341  of the wedge-shaped members  340  enter inside the free rear ends  120  of the wings  116  of the lancet case  102  immediately before the loading of the lancet assembly  100  into the injector  300 . Thereafter, when the lancet assembly is moved further backward, the rear ends of the wings  116  slide along and on the sloped surfaces  342  of the wedge-shaped members  340 , so that the wings  116  expand outward. Thus it is advantageous to provide the wedge-shaped members since it makes possible to automatically expand the wings  116  simply by inserting the lancet assembly rearward for setting. 
       FIG. 21  shows in a schematic perspective view the state of the lancet assembly  100  where the wings  116  are in the splayed out condition. It is noted that the lancet case  102  is shown with its near side half of the lancet case  102  is cut away for understanding the state of the lancet located inside the lancet case. As easily seen, the positions of the stoppers  122  are shifted outward because of splaying out of the wings  116  when compared with the state in which the wings are not splayed out (as shown for example in  FIG. 2 ). As a result, the stoppers  122  cannot function as the stoppers any more. Therefore, in the state shown in  FIG. 21 , when the lancet is to move forward, the the protruding portions  212  of the lancet body  204  do not hit the stoppers  122 , so that the forward movement of the lancet is not prevented. 
     After the loading of the lancet assembly  100  into the injector is completed described above, the lancet cap is removed. The weakened portion is broken by applying forces to the lancet body  204  and the lancet cap  206  in opposite directions around the extending direction of the pricking member, or pulling them so that these members are separated away from each other along extending direction of the pricking member. Then, when the lancet cap  206  is removed away from the lancet body  204 , the distal end portion of the pricking member  210  is exposed from the lancet body  204  (see  FIG. 12 ). In this way, the lancet cap performs a function of covering the distal end portion of the pricking member in advance. 
     In order to make it easy to twist off the lancet cap  206  by applying the force in the opposite directions around extending direction of the pricking member in the lancet case  102 , it is preferable that the lancet body  204  is formed with its cross section of which shape makes it impossible to rotate in the lancet case, while the rear portion of the lancet cap  206  located in the lancet case has a cross section of a shape that enables it to rotate in the lancet case. For example, in the case where the lancet case that accommodates the lancet body and the lancet cap has a rectangular cross section, the lancet body has a rectangular cross section that makes it impossible to rotate therein and the rear portion of the lancet cap has a circular cross section. 
       FIGS. 11 and 12  schematically show the state wherein the lancet cap is removed from the state shown in  FIGS. 9 and 10 , similarly to  FIGS. 7 and 8 . As seen from  FIG. 12 , the distal end portion  211  of the pricking member  210  is exposed in the lancet case, As seen from the comparison of  FIG. 11  with  FIG. 12 , the exposed tip of the distal end portion of the pricking member is located sufficiently back away from the front end opening  106  of the lancet case  102 . 
     As described above, the launching spring is kept in the compressed condition by the engagement of the protruding portion  324  of the plunger with the shoulder  330  of the trigger lever. Accordingly, in the state shown in  FIGS. 11 and 12 , the predetermined portion (for example, a finger tip) to be pricked is applied onto the front end opening  106  of the case body  114 , and then when the engagement of the trigger lever  328  is removed, the launching spring that has been compressed expands instantly. As a result, the plunger  310  moves forward so that the lancet body  204  with the distal end portion of the pricking member being exposed moves instantly forward and protrudes out of the front end opening  106  of the lancet case  102 , thereby pricking the predetermined portion applied thereto. 
     It is noted that the engaged state can be canceled by depressing the push button  350  downward, which is provided at the front end of the trigger lever. The trigger lever can rotate around a rotary shaft  326 , and may have a compressed spring under the push button  350 . In this case, when no force is applied to the button from its outside, an upward (thus, outward) force is applied to a portion of the trigger lever in front of the rotary shaft  326  as well as the bush button, while a downward (thus, inward) force is applied to a portion of the trigger lever behind the shaft. It is noted that by the similar action may be carried out by using the plate-like member  301  as described above, but reliability of such action is improved by using such spring. 
       FIGS. 13 and 14  schematically show the moment when the distal end portion  211  of the pricking member has just protruded from the front end opening  106  of the lancet case  102 , similarly to  FIGS. 7 and 8 . As seen from  FIG. 14 , the wings  116  are kept in the splayed out condition, the protruding portions  212  of the lancet body  204  have moved forward inside the stoppers  120  without being blocked by the stoppers  120 . 
     It is noted that a return spring is provided between the protruding portion  324  of the plunger  310  and a front partition  344  which is provided inside the housing and around the plunger  310 . This spring is such that it is compressed when the plunger  310  moves forward so as to launch the lancet. As a result, at the moment when the pricking is completed with the distal end portion  211  of the pricking member having protruded from the front end opening  106  of the lancet case  102 , or a time a little before or after such moment, the spring gets in the sufficiently compressed condition, and then it expands toward its original form, so that the lancet body is moved rearward after the pricking has been completed. 
       FIGS. 15 and 16  schematically show the state where the lancet body  204  has been moved rearward from the state shown in  FIGS. 13 and 14 , similarly to  FIGS. 7 and 8 . As easily seen from the comparison of  FIG. 12  with  FIG. 16 , the protruding portion  324  of the plunger has been in a fitting condition into a recess  348  located on the lower side of the trigger lever which recess is located behind a small protrusion  346  after having passed over the protrusion  346  by means of the expansion of the spring. By the provision of the protrusion  346  and the recess  348  in this way, the momentum of the plunger which is moving back is reduced, and the protruding portion  324  would not move forward over the protrusion  346  of the trigger lever even when the spring oscillation occurs in that the spring is compressed again after its expansion, which reduces a possibility of the second pricking. 
     In the state where the protruding portion  324  fits in the recess  348  which is located on the lower side of the trigger lever (in the shown embodiment, the side which is opposite to the side on which the push button is located) so to achieve the engagement condition, the protrusion  346  which is located in front of the recess  348  is configured such that such engagement is not removed even when a forward force is applied to the plunger. Specifically, a rear surface which defines the protrusion  346  (see  FIG. 14 ) extends at right angle to the pricking direction or at an angle near such right angle while the front surface  349  which defines the protrusion  346  (see  FIG. 13 ) extends obliquely with regard to the pricking direction to form a slope. When pressing the trigger button  350  for launching the lancet, the trigger lever rotates around the axis  326  and the protrusion  324  moves upward. 
     As a result, the protrusion  346  is not located on an orbit along which the protruding portion  324  of the plunger moves forward, so that it does not prevent the forward movement of the plunger. Then, the force applied to the trigger button is removed, the trigger lever returns to its original condition. 
     When such trigger lever is used, the engagement. relationship between the protruding portion  324  and the protrusion  346  or the fitting relationship of the protruding portion  324  in the recess  348  is kept even though an ejector applies a forward force to the lancet case and such force is applied to the plunger. In order to ensure such relationship, the front surface  325  which define the protruding portion  324  extends at a right angle to the moving direction of the plunger or at an angle near such right angle while the rear surface  327  extends obliquely to form a slope. 
     By combining the front surface  325  at the right angle and the oblique rear surface  327  which define such protruding portion  324  with the oblique front surface  349  and the right angle rear surface  347  which define the protrusion  346  on the lower edge of the trigger lever as described above, it is possible that the protruding portion  324  of the plunger can pass over the protrusion  346  of the trigger lever so as to move rearward, but once having passed over the protrusion  346 , the protruding portion  324  of the plunger cannot easily pass over the protrusion  346  of the trigger lever so as to move forward. In fact, in order to pass over the protrusion, at least a portion of the protruding portion or the protrusion has to substantially deform or break at least partly. 
     As shown in  FIGS. 7 to 16 , the injector according to the present invention comprises an ejector  312  in its lower side. Such ejector is schematically shown in  FIG. 22  in a perspective view. The ejector  312  comprises a base plate  351  and a pusher  352 , and is disposed in a lower portion of the injector housing  309 . The base plate  351  can be moved forward within the injector  300  by sliding the operation button  354  provided on the lower side of the base plate  351  from the outside of the injector in the direction of the arrow. For example, such a constitution may be employed as a guide channel  355  is provided on the inside of the injector housing and a rail is provided on the outside of the base plate for moving in the channel. 
     The plunger  352  is configured so that the front end portion  356  abuts against the rear end portion  108  of the lancet case  102  at the time when loading the lancet assembly  100  in the injector  300  is completed. As seen from the comparison of  FIGS. 7 and 8  with  FIGS. 9 to 16 , the shown embodiment is configures as such. In other embodiment, the plunger  352  may be so positioned as to be spaced from the rear end portion  108  of the lancet case  102 . It is noted that the pusher  352  is constituted so as to be capable of pushing forward the opposing side surfaces  128  of the case body  114  of the lancet case  102 , more preferably only the surfaces  130  which include the rear end edges of the side surfaces where the wings are absent. 
     When the state as shown in  FIGS. 15 and 16  is achieved after the completion of the pricking, the rear end surfaces  130  of the lancet case  102  is pushed forward with the pusher  356  by sliding the button  354  of the ejector forward. When the force which pushes forward exceeds a threshold force which makes the bumps  112  of the lancet case pass over the protruding portions  304  at the front end opening  302  of the injector  300 , the lancet case moves forward. 
     At this stage, the forward movement of the plunger is blocked by the protrusion  346  of the trigger lever and the recess  348  as described above. As a result, the force applied by the ejector is used first for moving the lancet case  102  forward, and then used for the disengagement of the rear end portion  202  of the lancet body  204  from the front end portion of the plunger as described below. The bump  218  of the rear end portion of the lancet body  204  (preferably a circumferential bump provided around the lancet body) in the lancet case  102  is pinched by the legs  320  and  322  of the front end portion of the plunger in the injector, so that the it is not moved forward. 
     When the lancet case  102  is moved forward as described, the rear end portions  120  of the wings  116  leave the wedge-shaped members  340 , so that the wings  116  elastically deform toward their original forms. That is, the splayed out wings close so as to achieve the state as shown in  FIG. 1 . In this way, the stoppers  122  provided on the inside of the wings  116  again function as the stopper. That is, the protruding portions  212  of the lancet body  204  cannot pass forward over the stoppers  122  in the lancet case. 
     Since the forward movement of the lancet body  204  with the distal end portion  211  of the pricking member  210  is prevented by the stoppers  122 , so that the distal end portion  211  of the pricking member can move forward only up to the position sufficiently away from the front end opening  106  of the lancet case  102 . of course, the protruding portions  212  cannot get out of the rear end opening of the lancet case  102 . In this way, when the lancet case  102  moves forward and the wings  116  return to their original forms, the lancet body is kept in the lancet case  102  while the protruding distal end portions  211  is sufficiently behind the front end opening  106 . 
       FIGS. 17 and 18  schematically show the state where the lancet case  102  is moving forward by means of the ejector  312 , similarly to  FIGS. 7 and 8 . As described above, the wings  116  have returned to their original forms. Therefore, the protruding portions  212  of the lancet body  204  prevented from their forward movement by the stoppers  122  of the wings  116 , and also from their rearward movement by means of the wall  132  which defines the rear end opening  107  of the lancet case  102 . 
     When the lancet case  102  is moved forward as shown, the protruding portions  212  of the lancet body  204  abut against the wall  132  which defines the rear end opening  107  of the lancet case  102 . It is noted that the forward movement of the plunger is prevented by the trigger lever. In such stage, a force applied in order to intend to move the pusher  356  forward. When the force is applied forward, such force is transferred to the bump  218  of the lancet body which is hold, namely grasped by the legs  320  and  322  of the plunger  310 , so that the bump  218  tries to splay the legs outward. When such force exceeds a certain threshold, the legs elastically splay outward, so that they release the bump  218  and the rear end portion of the lancet body  204  that they have grasped. It is noted that  FIGS. 15 to 18  show the state wherein the protruding portion  324  of the plunger is trapped in the recess  348  on the lower side of the trigger lever, and splaying out of the legs  320  and  322  is not prevented by the wall which defines the opening of the front partition  344  since the position of the front end portion  314  of the plunger is ahead of the front partition  344  of the housing. 
     When the ejector  312  is moved further forward from the shown state, the lancet case  102 , and therefore the lancet assembly is discharged from the injector  300  through its front end opening  302 . The lancet assembly that has been discharged is comprises the lancet case  102  and the pricking member of which distal end portion  211  is exposed, and the state of such lancet assembly is shown in  FIG. 23  similarly to  FIG. 2 . Easily seen, what is different from  FIG. 2  is that the lancet cap  206  is not present in  FIG. 23 . As described above, the protruding portions  212  of the lancet body  206  are sandwiched by the stoppers  122  and the wall  132  of the rear end opening, and cannot move while getting over these members. 
     As easily seen from  FIG. 23 , even in the case wherein the lancet body  204  is moved most forward, the tip of the pricking member is sufficiently away from the front end opening  106  of the lancet case  102 . Therefore, upon handling the lancet case  102  in the state as shown in  FIG. 23 , a risk is greatly reduced with respect to the exposed pricking member. 
     It is noted that the lancet body and he lancet case preferably have a means which makes the movement of the lancet body  204  smooth in the lancet case upon pricking. For example, as readily seen from  FIG. 23 , the lancet body  204  according to the present invention comprises other protruding portions  222 , and the lancet case  102  has the rails  140  on the inside surface thereof so as to sandwich the protruding portions. By combining the protruding portions and the rails, a guide means may be formed which makes the movement of the lancet body  204  in the lancet case  102 . 
     It is preferable that the lancet assembly and the injector are formed of a resin, and particularly resin molded articles except the pricking member and the springs. Such molded articles are preferable as to the function of the wings, the function of the plunger legs, and the relationships between the protruding portions  112  of the lancet case and the bumps at the front end opening of the injector in addition to the ease of production thereof. 
     In one embodiment of the injector according to the present invention, it comprises a pricking depth adjusting drum  360  disposed behind and adjacent to the rear partition  358  in the injector housing (see for example  FIG. 7 ). A ring-shaped member  361  having an opening  363  is positioned in the inside of the front end of the drum  360  (these member are preferably connected together), and the rear end portion  362  of the plunger extends through the opening  363 , and the rear end portion  362  has a hitting member  365 . Further, the ring-shaped member is able to rotate around such plunger. Specifically, when a rotating knob  369  which is fitted in the rear end of the drum  360  is rotated, the drum  360  and the ring-shaped member  361  are able to be rotate around the plunger. 
       FIG. 24  schematically show the ring-shaped member located around the plunger and the hitting member  365  located at the rear end of the plunger in a perspective view with omitting the plunger (only of which extending direction is indicated with a broken line). The length (a) of the ring-shaped member  361  in the pricking direction changes along the circumferential direction thereof continuously or stepwise. In the embodiment illustrated, the length in the pricking direction changes stepwise for example as a 1 , a 2 , and a 3 . The hitting member  365  has on both sides thereof an upper hitting portion  367  and a lower hitting portion  367 ′. When the lancet is launched and the plunger moves forward, the hitting member  365  moves in the pricking direction as indicated by the arrow, and strikes the ring-shaped member. 
     In the embodiment shown in  FIG. 37 , for example, when the plunger moves forward, the hitting portion  367  strikes the step  371 ′ of which length along the pricking direction is al. That is, the hitting portion strikes one of the steps that constitute portions of the rear end surface of the ring-shaped member. When the knob  369  is turned a little clockwise (seeing from the left hand side in the drawing) as indicated by the arrow in the drawing in this state, the upper hitting portion  367  is moved to the near side, and the lower hitting portion  367 ′ is moved to the further side. 
     As a result, the hitting portion  367  is allowed to strike the step  373  having a length a 2  in the pricking direction, and the hitting member  367 ′ is allowed to strike the step  373 ′ having a length a 2  in the pricking direction. As easily understood, as the lengths in the pricking direction of the ring-shaped member which the hitting portion strikes are different, for example the length in the pricking direction is different between step  371  and step  373 , the distance over which the plunger can travel forward, namely the pricking depth changes. 
     In the case wherein at least one of the hitting member  365  and the ring-shaped member  361  is formed from an elasticity rich material such as a silicone, an urethane or the like so that it has an impact relieving property, the impact generated by these members when hitting can be mitigated. This provides an advantage of mitigating the impact which the user feels upon the pricking operation. 
     INDUSTRIAL APPLICABILITY 
     The lancet, the lancet case and the lancet assembly constituted from these members and the injector of the present invention provide a safer and convenient device.