Abstract:
A method of staging a tissue sample cassette, including a cassette body and a lid, from an upper position in a frame used during a tissue embedding process to a lower position in the frame. The method comprises coupling the cassette with the frame such that the cassette is in the upper position and positively stopped at the upper position by first structure on a wall of the frame. The cassette is moved relative to the frame to the lower position by selectively engaging the cassette with a staging mechanism. An external force is applied to the cassette with the staging mechanism in a direction to move the cassette from the upper position toward the lower position. The cassette is retained in the lower position using second structure on the wall of the frame, such that the cassette is exposed for embedding the cassette in an embedding medium and subsequently slicing the tissue sample embedded in the embedding medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of application Ser. No. 12/836,102, filed Jul. 14, 2010 (pending), which is a divisional of application Ser. No. 11/072,119, filed Mar. 4, 2005 (now U.S. Pat. No. 7,776,274) which is a continuation of PCT Serial No. PCT/US02/30775 filed on Sep. 26, 2002 (expired), the disclosures of which are hereby fully incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to supports for handling and embedding tissue samples for pathological analysis and, more particularly, to cassettes which can receive one or more tissue samples and be embedded and subsequently microtomed with the tissue sample or samples. 
       BACKGROUND OF THE INVENTION 
       [0003]    To accurately diagnose various tissue diseases and conditions, medical personnel must remove one or more samples of tissue from the body of a patient. This process of harvesting tissue from the body is known as a biopsy. Once the tissue sample or samples are removed and sent to a pathology laboratory, the tissue will go through a series of procedures performed by a histotechnician and, ultimately, a pathologist, in order to diagnose the tissue. The present invention generally relates to those procedures that are normally performed by the histotechnician to prepare the tissue sample or samples into slides that may be analyzed under a microscope by the pathologist. 
         [0004]    Although the singular term “sample” is used throughout this specification, it should be understood that this term likewise encompasses plural “samples” as well. Once a tissue sample is removed from the body of a patient, it is typically placed into a specimen container containing a tissue fixative solution and then the container is transported to a pathology laboratory. The tissue will undergo a process known as “grossing-in” in the pathology lab during which a histotechnician will retrieve the tissue sample from the container, typically cut the tissue into appropriate sizes for tissue processing, place individual samples into the appropriate sized small plastic tissue cassettes, and assign tracking numbers to each cassette. These tracking numbers are then logged into a tracking system used in the laboratory. For the smallest tissue samples, which may only be scrapings, the cassette will have fine mesh openings on the sides and bottoms. In other situations involving very small tissue samples, the samples are placed into a bag that resembles a tea bag and prevents the smallest tissue samples from escaping. Larger tissue samples are placed into cassettes having somewhat larger slotted openings which are again smaller than the tissue sample inside the cassette. 
         [0005]    The cassettes are then placed into a stainless steel perforated basket and run through a tissue processing machine, often overnight. This machine uses a combination of vacuum, heat, and chemicals to remove the interstitial fluids. Once the fluids have been removed from the tissue samples, the processing machine immerses the tissues samples in a bath of molten paraffin so that the interstices in the tissue are replaced with paraffin. The histotechnician then removes the basket from the machine and removes the individual tissue cassettes. At an embedding station, which has a molten paraffin reservoir and dispenser, the histotechnician will individually remove the tissue from each cassette. The histotechnician must carefully orient the tissue sample, based on tissue type, into a stainless steel base mold which is roughly the size of the tissue cassette and is partially filled with molten paraffin. The tissue sample must be manually held, typically using forceps, against the bottom of the mold. If it is not, this could compromise the ability to make proper slices of the tissue later in the microtome. The molten paraffin is then rapidly cooled on a refrigerated plate, which may be a thermal electric cooler (TEC), to partially solidify the paraffin thereby holding the tissue sample in the proper orientation against the bottom of the mold. The cassette is then placed on top of the base mold and paraffin is poured through the opened top of the cassette into the base mold. The cassette changes its function at this point in the procedure from a tissue holding component to a fixation device for later use in taking shavings or slices from the solidified paraffin in a microtome. The base mold is chilled until all of the molten paraffin has solidified and the histotechnician removes the stainless steel base mold from the block of embedded paraffin. The tissue sample is thus embedded within a rectangular block of paraffin with a plastic tissue cassette on the opposite side which will then be used as a holder in the chuck of the microtome. As with the tissue processing machine, the embedding process is accomplished in a batch fashion during which an average histotechnician may embed approximately 40 to 60 cassettes per hour. 
         [0006]    The blocks of hardened paraffin containing the embedded tissue samples are then ready to be sliced into extremely thin sections for placement on a microscope slide. The histotechnician mounts the embedded tissue block in a chuck on the microtome which is sized to accept the side of the block that has the embedded plastic cassette. The histotechnician can then begin slicing the paraffin block which has the tissue sample embedded opposite to the plastic cassette surface. This yields a ribbon of individual slices of the tissue embedded in the paraffin. The action of the microtome causes the individual slices to stick together when done properly and, subsequently, these very thin ribbons of slices are floated into a water bath and a glass slide is carefully placed underneath the slice. The slice, with the thin sectioned tissue sample embedded therein, is then adhered to the top of the slide. 
         [0007]    When the histotechnician has enough slides from the tissue sample, the slides are placed into an automatic staining machine. The staining machine goes through a series of infiltrating steps to stain the different tissue and cells of the slide different colors. This helps the pathologist identify different structures and makes it easier to find any abnormalities in the tissue. After the staining procedure is complete, the slides are cover slipped and prepared for the pathologist to place under a microscope to analyze. 
         [0008]    Based on the summary of the procedure provided above, it will be appreciated that conventional tissue sample handling and processing is a very labor-intensive process involving several manual steps performed by a histotechnician. Thus, repetitive stress injuries such as carpal tunnel syndrome are prevalent. This is especially true with the tissue sample embedding process. These multiple manual operations and repeated tissue handling increase the likelihood of human error and, moreover, require highly trained and skilled histotechnicians to ensure that the tissue samples ultimately adhered to the slides for analysis by the pathologist are in an optimum condition and orientation to make accurate diagnoses. 
         [0009]    U.S. Pat. No. 5,817,032 (the &#39;032 patent) discloses various improvements to this area of technology, including new manners of holding tissue samples during the grossing in, embedding, and microtome or slicing procedures. More specifically, the &#39;032 patent relates to a tissue trapping and supporting device, which may be a cassette, and which may be cut with a microtome. When a cassette is used, the tissue sample is immobilized within the cassette and subjected to the process for replacing tissue fluids with paraffin. Then, the tissue sample and the cassette are sliced at the same time for mounting on microscope slides. Because the tissue sample is never removed from the cassette from the time it is processed in the tissue processing machine to the time that it is cut with the microtome, a significant amount of handling time is saved. Moreover, the chance for human error or tissue loss due, for example, to dropping the tissue during handling, is significantly reduced due to the elimination of separate tissue handling steps. This patent also generally discusses an automated process which, in conjunction with the novel tissue cassettes, even further reduces the handling steps during the entire procedure. 
         [0010]    In spite of the various advances made in this field, there is an increasing need for additional improvements related to increased production capability and increased and more consistent quality of embedded tissue samples and resulting slices or ribbons of embedded tissue which will be subject to diagnosis. 
       SUMMARY OF THE INVENTION 
       [0011]    Generally the invention relates to a cassette for holding a tissue sample during an embedding and microtoming or slicing process. The cassette includes a body with a bottom wall and a plurality of side walls extending upwardly with respect to the bottom wall to define an interior space for receiving the tissue sample. The bottom wall and the plurality of side walls are constructed of a material capable of being sectioned in a microtome. Preferably, the cassette material is also resistant to any type of degradation during processing which would compromise its ability to function in accordance with the invention. In a first aspect of the invention, the plurality of side walls comprise first and second side walls on opposite sides of the bottom wall each including portions angling from approximate midpoints of the first and second side walls toward the other of the first and second side walls on the opposite side of the bottom wall. In the preferred embodiment, the two longest side walls of the four side walls comprising a rectangular cassette are generally V-shaped in a direction away from the interior of the cassette. This presents an apex of the V-shape to the microtome blade, after the embedding process is complete, which assists with the cutting action. Specifically, this feature has been found to reduce or prevent the hardened paraffin from breaking or cracking away from the cassette side wall material while making slices in the microtome. 
         [0012]    The cassette preferably further includes a lid configured to be coupled with the body for movement between open and closed positions. The lid may be depressed downwardly on top of the tissue sample in the cassette interior. The lid is preferably stiffer than the bottom wall of the cassette. This feature allows the lid to position the tissue sample in the cassette parallel to the bottom of the mold during the embedding process. More specifically, the stiffer lid pushes the tissue sample and the more flexible bottom wall of the cassette against the rigid bottom of a base mold while the molten paraffin solidifies. This helps ensure that the bottom wall of the cassette can be removed in its entirety during a facing operation in the microtome prior to slicing the tissue sample, and that the tissue is positioned flatly against the bottom wall of the cassette. 
         [0013]    In another aspect of the invention, the side walls of the cassette are perforated such that there is at least a ratio of about 2.5:1 of open area to solid material area whereby the solidified paraffin occupies the open area of the side walls. This ratio may be altered by using different materials for the cassette and/or paraffin embedding media. For instance, a higher molecular weight paraffin or lower moneluculer weight cassette will allow the ratio to vary somewhat. Currently, an industry standard paraffin (e.g., Sakura VIP processing/embedding medium) works best with a ratio of at least about 3.0:1 and, more preferably, at least about 3.5:1. This reduces the amount of cassette material that must be cut by the microtome blade while taking slices of the tissue and, therefore, increases blade life and quality of the resulting ribboned, embedded tissue samples. In addition this ratio assures that the paraffin is strong enough not to fracture when cut by the microtome blade. Another feature that results in similar advantages involves forming the side walls from ribs and offsetting the ribs of one of the first and second side walls with respect to those of the opposite side wall along the side wall length. Thus, the microtome blade will contact a more uniform amount of the cassette material along its length during each pass. This significantly reduces blade wear while cutting through the cassette material. Reduced blade wear is advantageous to keeping blade costs under control as the majority of blades used are disposable. 
         [0014]    In another aspect of the invention, the cassette further includes a flange extending along upper portions of at least two of the side walls. The flange includes depressions configured to register with detents in a frame during the tissue embedding process. This increases the effective height dimension of the cassette interior, thereby allowing more tissue to be placed in the cassette and more passes to be made in the microtome. In this regard each pass of the microtome may only take a 5 micron slice. Therefore, using depressions having a depth, for example, of 0.14″ can allow about 70 more slices to be taken in the microtome. 
         [0015]    The invention further contemplates the various unique assemblies of two or more of the tissue cassette, frame, and base mold as disclosed herein. With respect to the frame and base mold, for example, structure is provided to physically hold the frame against the base mold. In the preferred embodiment, a seal is provided to perform this holding function and also to prevent leakage of liquid paraffin from the base mold. 
         [0016]    In another aspect, the invention contemplates a device for staging a tissue sample cassette from an upper position in a frame used during a tissue embedding process to a lower position in the frame. The device includes a handle, a staging mechanism coupled with the handle and configured to engage an upper surface of the cassette, and a stop operatively coupled to the handle and configure to stop vertical movement of the staging mechanism when the cassette reaches the lower position in the frame. The staging mechanism further comprises a plurality of fingers which are configured to engage a corresponding plurality of locations on the upper surface of the cassette. For example, four fingers may be provided for engaging four corner locations on the cassette. This helps ensure that the cassette is engaged with at least four pairs of detents located proximate corner portions of the cassette thereby positioning the bottom wall of the cassette parallel to and against the bottom wall of the base mold. 
         [0017]    In one embodiment, the staging device is a rigid member and the stop comprises a fixed stop member coupled for movement with the staging mechanism and configured to stop against an upper surface of the frame. In another embodiment, the device includes a stabilizing mechanism coupled with the handle and moveable relative to the staging mechanism. The stabilizing mechanism is configured to engage an upper surface of the frame as the staging mechanism moves the cassette from the upper position to the lower position within the frame. In this embodiment, the staging mechanism is normally spring-biased into an upward position and is forced downward against the spring bias when moving the cassette from the upper position to the lower position. The stop in this embodiment further comprises respective surfaces of the handle and stabilizing mechanism which engage one another when the staging mechanism has placed the cassette into the lower position. The staging devices of this invention ensure that the cassette is fully staged into the base mold, while ensuring that the cassette is not pushed too far through the frame. Moreover, the staging devices ensure that the bottom wall of the cassette and, therefore, the tissue sample, lay flat against the bottom of the base mold. This improves the efficiency and quality of tissue shavings later made in the microtome. 
         [0018]    The invention also encompasses the various methods of using the tissue cassette and cassette/frame/base mold assemblies as disclosed herein. 
         [0019]    These and other objects, advantages, and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is an exploded perspective view of an assembly including the tissue cassette, the frame into which the cassette is inserted and the base mold into which the frame and cassette assembly are inserted. 
           [0021]      FIG. 2  is an assembled perspective view of the tissue cassette, frame and base mold. 
           [0022]      FIG. 3  is a cross sectional view taken along line  3 - 3  of  FIG. 2  and showing the tissue cassette in its initial upper position. 
           [0023]      FIG. 4  is an assembled perspective view, similar to  FIG. 2  but illustrating the second, staged position of the tissue cassette. 
           [0024]      FIG. 5  is a cross sectional view taken along line  5 - 5  of  FIG. 4  and showing the tissue cassette staged down into its second, lower position against the bottom of the base mold. 
           [0025]      FIG. 6  is a cross sectional view of the frame and the tissue cassette embedded in material such as paraffin, after release from the base mold. 
           [0026]      FIG. 7  is a perspective view of a manual, spring-biased staging device. 
           [0027]      FIG. 8  is a longitudinal cross sectional view of the staging device of  FIG. 7  being used to stage a tissue cassette through the frame and into the base mold. 
           [0028]      FIG. 9  is a perspective view of a tissue cassette constructed in accordance with a second embodiment of the invention. 
           [0029]      FIG. 10  is a cross sectional view taken along line  10 - 10  of  FIG. 9 . 
           [0030]      FIG. 11  is a perspective view of a manual staging device constructed in accordance with a second embodiment. 
           [0031]      FIG. 12  is a bottom perspective view of the staging mechanism associated with the staging device of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Turning first to  FIGS. 1-3 , a tissue cassette  10  constructed in accordance with the invention is received within a frame  12  and the tissue cassette  10  and frame  12  are then positioned in a base mold  14 . After a staging operation the base mold  14  is subsequently filled with liquid paraffin, as described further below. Tissue cassette  10  includes a perforated body  20  formed by four side walls  22   a,    22   b,    22   c,    22   d  and a bottom wall  24 . Each wall is preferably constructed with perforations or openings  26  and ribs  28 . An upper flange  30  surrounds and extends outwardly from the respective side walls  22   a - d . A lid  32  is attached to body  20  by a hinge  34  which allows vertical movement of lid  32  into the interior of body  20  for retaining one or more tissue samples against bottom wall  24 . Lid  32  is likewise formed with perforations  36  which may be elongated and generally separated by ribs  38 . As shown best in  FIG. 1 , elongated perforations  26 ,  36  on the bottom wall  24  and lid  32  respectively extend toward central areas  24   a,    32   a  of the bottom wall  24  and lid  32 . This assists with allowing a mold (not shown) to fill with material, such as PFA, during the molding process of cassette  10 . 
         [0033]    Lid  32  is formed with a shape along its circumference which compliments the shape of side walls  22   a - d . In this regard, respective lengthwise side edges  40   a,    40   b  of lid  32  are formed in the shape of a shallow “V” and each includes an apex  42   a,    42   b  generally at the central portion thereof. This likewise corresponds to the lengthwise shallow “V” shape of side wall  22   a  and opposite side wall  22   c.  Thus, when the embedded tissue cassette is later placed in a microtome and sections are sliced from the embedded tissue cassette, the microtome blade will initially contact the apex corresponding of side wall  22   a  or  22   c,  depending on which side is facing up in the microtome. This has been found to increase the quality of ribboned slices being made from the embedded tissue cassette. That is, little or no fracturing of paraffin will occur at the paraffin/cassette interfaces. 
         [0034]    Frame  12  more specifically includes an open interior  50  which receives cassette  10 , and an angled front wall  52  which may be used for recording indicia, such as patient data. Respective upper and lower sets of detents  54 ,  56  and  58 ,  60  extend inwardly into the open interior  50  of frame  12 . Initially, tissue cassette  10  is held between the upper pairs of detents  54 ,  56  by pressing the upper flange  30  downwardly past the upper sets of detents  54  and against the lower set of detents  56  after one or more tissue samples have been placed into cassette body  20  and lid  32  has been closed. Respective detents  61  extend inwardly from side walls  22   a - d  to allow lid  32  to be snapped and retained in a closed position. During a staging operation, tissue cassette  10  will be moved vertically downwardly through frame  12  until flange  30  snaps past detents  58  and rests against detents  60  at a lower position ( FIG. 5 ). Recesses  62 ,  64  are formed in at least two opposite side walls for allowing fingers of a gripper mechanism to register with the assembly during automated handling and embedding operations, as necessary. Preferably side walls  66   a,    66   b  contain these recesses  62 ,  64 , while additional side walls  66   c,    66   d  may include additional structure allowing automated handling, or allowing other functions as necessary. Base mold  14  includes an open interior  70  for receiving frame  12  and may be surrounded by a resilient elastomeric seal  72  which prevents the escape of liquid paraffin during the embedding process. This eliminates an additional step of scraping off excess hardened paraffin from frame  12  after the embedding process is complete. Such excess paraffin can prevent the frame from properly fitting in a microtome chuck. 
         [0035]    By comparing  FIGS. 2 and 3  to  FIGS. 4 and 5 , it will be appreciated that during the staging process, tissue cassette  10  is moved vertically downward into the interior  70  of base mold  14  such that the bottom  24  of tissue cassette  10  contacts the bottom  74  of base mold  14 . At this position, flange  30  of tissue cassette body  20  is received between respective detents  58 ,  60  holding it in this lower position. Frame  12  is preferably press fit and held frictionally within base mold  14  by one or more resilient seals  72 . Seal  72  performs two functions in this embodiment. First, it physically holds frame  12  within base mold  14  by friction. This prevents the frame  12  and attached cassette  10  from floating or otherwise moving while base mold  14  is filled with paraffin. Second, it prevents the liquid paraffin from escaping from base mold  14  in the area between outer walls  12   a  of frame  12  and interior  70  of base mold  14 . It will be appreciated that a holding member other than seal  72  may be used instead to physically hold frame  12  against base mold  14 . In this case, seal  72  may not be necessary. As some examples, such holding members may be clamps, fasteners, spring members or weights. In these figures, the tissue sample or samples within cassette  10  have been deleted for clarity. However, it should be understood, that lid  32  will be depressed down onto one or more tissue samples  80  contained with the interior of cassette body  20  ( FIG. 6 ). While the assembly of cassette  10 , frame  12  and base mold  14  is in the staged configuration shown in  FIGS. 4 and 5 , liquid paraffin is introduced through the open interior of frame  12  and through the perforations  26 ,  36  of cassette  10  into the interior  70  of base mold  14 . The liquid paraffin is then preferably cooled on a suitable cooling device, such as a TEC, and the assembly of the tissue cassette  10 , frame  12 , embedded tissue sample  80  and hardened paraffin  82  is removed from base mold  14  as shown in  FIG. 6 . Frame  12  may then be used as a device to fix the assembly in a microtome chuck and slices are then taken from the bottom surface  82   a  of paraffin  82 . Initially, a facing blade is used to remove the initial layer of paraffin  82  and bottom wall  24  of tissue cassette  10 . At this point, a different microtome blade may be used to take ribboned slices or shavings of tissue sample  80  and the surrounding paraffin  82  and side walls  22   a - d  of tissue cassette body  20 . Often times the same blade that is used for facing may also be used for sectioning. 
         [0036]      FIGS. 7 and 8  illustrate one type of staging device  100  which may be used in conjunction with the tissue cassette  10 , frame  12  and base mold  14  described above. Staging device  100  includes a handle  102  at an upper end and a staging mechanism  104  at a lower end. Staging mechanism  104  is coupled to a hollow cylinder  106  extending upwardly into a shroud  108  rigidly connected with handle  102 . A plurality of four stabilizer members  110  are rigidly coupled with cylinder  106 , while a plurality of preferably movable staging fingers  112  are coupled to a reciprocating shaft  114  which extends through cylinder  106 . Shaft  114  is rigidly connected to handle  102  and is biased therewith in an upward position by a spring  116  positioned between a bottom surface  102   a  of handle  102  and an upper surface  106   a  of cylinder  106 . Thus, it will be appreciated that stabilizer members  110  may be placed against an upper side of frame  12  for stabilizing purposes and handle  102  may then be depressed downwardly as indicated by arrow  118 . This moves reciprocating shaft  114  and the attached staging fingers  112  downwardly against tissue cassette  10  thereby moving the tissue cassette  10  relative to frame  12  from its upper position shown in  FIG. 3  to its lower, staged position shown in  FIG. 5 . To avoid pushing cassette  100  too far through frame  12 , surface  108   a  stops against surface  110   a  as flange  30  reaches its lower position between detents  58 ,  60 . 
         [0037]      FIGS. 9 and 10  illustrate a second embodiment of a tissue cassette  120 . Tissue cassette  120  includes a cassette body  122  having four side walls  124   a - d  surrounding an open interior and bounded on a bottom side by a bottom wall  126 . Side walls  124   a - d  are constructed of ribs  128  separated by perforations  130  and bottom wall  126  is constructed by ribs  132  separated by perforations  134 . Ribs  128  of side wall  124   a  are offset in a lengthwise direction relative to ribs  128  of opposite side wall  124   b,  as shown by distance “d” in  FIG. 10 . Distance “d” may vary, however, in this embodiment, on average, it is approximately 0.015″ to 0.030″. Offsetting ribs  128  in this manner ensures that a microtome blade passing through walls  124   a  and  124   b  contacts a more uniform amount of cassette material along its length. This leads to longer blade life, more uniform blade wear and more consistent high quality slices of embedded tissue. Ribs  132  and perforations  134  extend in their lengthwise direction toward a central area  126   a  of bottom wall  126 . In this preferred embodiment, side walls  124   a - d  are constructed such that the ratio of plastic cassette material, such as PFA, to the open area formed by perforations  130  is approximately 3.7:1. To achieve at least this ratio in the preferred embodiment, ribs  128  have a width w 1  of approximately 0.010″ to 0.014″ while perforations  130  have a width w 2  of approximately 0.040″ to 0.050″. This perforated area, which is below solid side wall portion  136  is the area which will be cut with a microtome blade after embedding of tissue sample  80  ( FIG. 6 ). Especially when using PFA with a Shore D hardness of 48 to 55 as the material for cassette  120 , in combination with the industry standard paraffin embedding material mentioned above, this ratio of cassette material to open area has been found to improve the quality of cuts made through the embedded cassette and increase blade life significantly. Depending on the respective molecular weights of the embedding material and the cassette material, this ratio may be increased or reduced. 
         [0038]    A flange  140  surrounds the upper side of cassette body  122  and contains respective upwardly facing depressions  142   a,    142   b,    142   c,    142   d.  A number of downwardly facing depressions  142   e,    142   f  (only two of several referenced) are also contained in flange  140 . These depressions respectively register with at least detents  54 ,  56  and  58 ,  60  of frame  12  (see  FIGS. 3 and 5 ). It will be appreciated that additional lower detents may be formed on frame  12  to provide further support and prevent cassette  10  from being pushed too far through frame  12 . In such a case, additional depressions are formed in the underside of flange  140  to accommodate the additional supportive detents. The depressions allow the effective outward extension of cassette body  120  from frame  12  to be increased thereby increasing the number of slices that may be taken from the embedded cassette in a microtome. This can be important in many situations in order to obtain the desired slides for pathologic examination. 
         [0039]    Detents  144  are also formed on side walls  124   a - d  for retaining a lid  150  in place. Lid  150  is coupled to cassette body  122  by a hinge  152 . Lid  150  is formed to be stiffer than bottom wall  126  of cassette body  122  so that lid  150  may be used to press the tissue sample against the bottom wall  126  and to press the bottom wall  126  against the rigid bottom  74  of base mold  14  ( FIG. 5 ). Lid  150  is formed by a plurality of ribs  154  generally separated by perforations  156  and each extending in a lengthwise elongated fashion toward a central area  150   a  of lid  150 . Lid  150  further includes side edges  158   a,    158   b  extending lengthwise thereon and having a shallow “V” shape with a central apex  160   a ,  160   b.  Angle V ( FIG. 10 ) is preferably about 4°. As with the first embodiment, the shape of side edges  158   a,    158   b  complements similar shape of side walls  124   a,    124   b  of cassette body  122 . In this regard, these side walls  124   a,    124   b , either one of which may be the initial wall cut in the microtome, include respective apecies  162   a,    162   b.  Respective ends  164   a,    164   b  of lid  150  also complement the similar shape of cassette body side walls  124   c,    124   d  to achieve a close fit of lid  150  within cassette body  122 . The use of cassette  120  in the process of embedding one or more tissue samples, including the staging process within frame  12  and the embedding or molding process within base mold  14  is the same as described above with regard to  FIGS. 1-8 . 
         [0040]      FIGS. 11 and 12  illustrate a manual staging device  200  in accordance with a second embodiment. Staging device  200  comprises an upper handle  202  and a lower staging mechanism  204  coupled together rigidly by a shaft  206 . In  FIG. 12 , handle  202  and shaft  206  have been deleted for clarity. Staging mechanism  204  preferably comprises a plurality of four staging members  210 ,  212 ,  214 ,  216  extending generally radially outward from shaft  206  and each including a finger portion  210   a,    212   a,    214   a,    216   a.  The finger portions  210   a - 216   a  respectively engage upper corner portions of cassette  10  ( FIG. 1 ) or cassette  120  ( FIG. 9 ). When the user then pushes downward on handle  202 , finger portions  210   a - 216   a  urge cassette  10  or cassette  120  downward into the lower, staged position ( FIG. 5 ). To prevent the cassette from being moved too far downward, a pair of stops  218 ,  220  are provided on staging mechanism  204 . In this embodiment, stop surfaces  218   a,    220   a  stop against the upper surface of frame  12  as cassette  10  or cassette  120  reaches the lower, staged position ( FIG. 5 ). Thus, the distance between the lower ends of finger portions  210   a - 216   a  and stop surfaces  218   a,    220   a  equates to the distance between upper detent pair  54 ,  56  and lower detent pair  58 ,  60 . It will be appreciated that other forms of staging mechanisms and stops may be provided while falling within the spirit and scope of the invention. 
         [0041]    While the present invention has been illustrated by the description of the various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicant&#39;s general inventive concept.