Abstract:
An automated slide stainer with slides mounted in a horizontal position on a rotary carousel. Reagents and rinse liquids are automatically dispensed onto tissue sections or cells mounted on slides for the purpose of performing chemical or immunohistochemical stains. The rinse liquids are removed by an aspiration head connected to a source of vacuum. Individual slides or groups of slides are supported on flat heating stations for heating to individual temperatures. Temperature control electronics on the carousel are controlled by a user interface off of the carousel.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a divisional of U.S. application Ser. No. 10/027,746, filed Dec. 20, 2001, which is a continuation of U.S. application Ser. No. 09/688,619, filed Oct. 16, 2000, now U.S. Pat. No. 6,541,261, which is a divisional of U.S. application Ser. No. 09/032,676, filed Feb. 27, 1998, now U.S. Pat. No. 6,183,693. The entire teachings of the above applications are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Tissue sections or cellular monolayers are commonly examined by microscopic examination, for both research and clinical diagnostic purposes. Thin tissue sections or cellular preparations are commonly 1-10 microns thick, and are nearly transparent if untreated. In order to visualize various histologic features, a wide array of staining procedures have been developed over the years that highlight various cellular or extracellular components of the tissues. Histochemical stains, also commonly termed “special stains,” employ chemical reactions to color various chemical moieties. Immunohistochemical stains employ antibodies as probes to color specific proteins, commonly via enzymatic deposition of a colored precipitate. Each of these histochemical and immunohistochemical stains requires the addition and removal of reagents in a defined sequence for specific time periods, at defined temperatures. Therefore, a need arises for a slide stainer that can perform a diversity of stains simultaneously under computer control, as specified by the technologist.  
           [0003]    An early slide stainer for immunohistochemistry was described by David Brigati M.D., U.S. Pat. No. 4,731,335. In that disclosure, microscope slides were closely apposed to each other, to form capillary gaps. The pairs of slides were mounted in a holder that could be moved about by a mechanical arm along three axes. If slides were to be heated, all of the slides were moved as a group into a humidified heated chamber. Therefore, random access capability is not possible with this design.  
           [0004]    In another slide stainer by Rogers and Sullivan, U.S. Pat. No. 4,043,292, slides are mounted on a rotary carousel. Their invention heats the slides by passing a heated stream of air over the slides. All of the slides are heated to the same temperature.  
           [0005]    Wooton, McLeod, and Read disclose another slide stainer that incorporates heat capability, in U.S. Pat. No. 5,231,029. In that invention, a steam chamber is provided to heat slides. The humidity in the steam chamber is designed to be just below 100 percent. If the slides are to be heated, they are placed into the chamber. Since the slides are either in or out of the chamber, all slides must be brought to the same heated temperature, a temperature approximately that of steam (100° C.).  
           [0006]    A recently described batch slide stainer commercialized by Ventana Medical Systems, Inc. is disclosed in U.S. Pat. No. 5,595,707 by Copeland, et. al. In that disclosure, slides are placed on a rotary carousel that allows for the addition and flushing of reagents from the slide surface. Their slide stainer includes a heating chamber that is heated by the introduction of warm air. A temperature sensor is contained within the chamber for providing temperature feedback to a microprocessor. Similar to the other slide stainers described above, all slides must be brought to the same temperature.  
         SUMMARY OF THE INVENTION  
         [0007]    This invention relates to an improved slide staining device, for the application and removal of reagents to biologic tissue sections mounted on microscope slides. The improvement relates to the random access capability of the slide stainer, i.e., one that performs any of a list of procedures to any of a plurality of biologic samples mounted on microscope slides. Since various procedures require heat at different times to enhance the rate of chemical reaction, a means has been developed to heat slides to different temperatures, independently of the temperatures of other slides. This invention allows for heating each slide to its own specified temperature.  
           [0008]    Any of the previously-described systems could potentially be modified to duplicate their heater control systems to provide for multiple levels of heating control. For example, commercial thermal cyclers are now available that incorporate four different heating blocks that share the same microprocessor. However, the type of hard-wired temperature control mechanism that heats and cools four different blocks would be expensive and cumbersome as the number of independent samples increases. For example, in the preferred embodiment of the present invention, forty-nine independent heating positions are described. If we assume that two wires provide power to the heater, and two wires provide temperature feedback from each heating sensor, then a total of 196 wires would need to be connected between the different heaters and the computer control circuitry. Placing all of these wires on a service loop between a stationary computer and a moving slide stainer presents yet another difficulty, increasing the cost of manufacture and servicing.  
           [0009]    In accordance with one aspect of the invention, a moving plating, preferably a carousel, is adapted to support a plurality of microscope slides bearing biological samples. In particular, a plurality of flat heating stations are provided on the platform, each heating station supporting at least one microscope slide and, in a preferred embodiment, each heating surface supporting a single microscope slide. The heating stations are individually controlled to control temperatures to which the slides are heated.  
           [0010]    According to another aspect of the invention, a plurality of heaters that can each heat at least one slide are associated with a moving platform that is adapted to support a plurality of microscope slides. Each heater includes a heating element set, each set having at least one heating element. A temperature controller electronic circuit mounted on the moving platform provides electrical power to the heating element such that each heating element set can be heated to a different temperature. A user interface mounted off of the moving platform specifies the desired temperatures for the microscope slides through a communication link with the temperature controller electronic circuit.  
           [0011]    Preferably, the communication link is a group of wires, the number of wires being fewer than the number of heating elements. To that end, the temperature controller electronic circuit may include a shift register which receives control data from the user interface, multiple shift registers of plural controllers being daisy chained. Individual temperature sensors may also be provided to provide temperature feedback information to the temperature controller electronic circuit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0013]    [0013]FIG. 1 is a perspective view of a first embodiment of a slide stainer.  
         [0014]    [0014]FIG. 2 is a top view of a slide frame for providing five sealed cavities above five different slides holding tissue samples.  
         [0015]    [0015]FIG. 3 is a top view of a slide frame base.  
         [0016]    [0016]FIG. 4 is a bottom view of a slide frame housing.  
         [0017]    [0017]FIG. 5 is a top view of the slide frame housing with five microscope slides in their appropriate positions, showing the area to which heat is applied.  
         [0018]    [0018]FIG. 6 is a cross-sectional view of a slide frame resting on the slide rotor.  
         [0019]    [0019]FIG. 7 is a schematic diagram of the heater and sensor wiring diagram, on the slide frame, and the interconnection with the temperature controller.  
         [0020]    [0020]FIG. 8 is a side cross-sectional view of a cartridge pump dispensing mechanism in the liquid dispensing and removal station.  
         [0021]    [0021]FIG. 9 is a side cross-sectional view of a bulk liquid dispensing station housed in the liquid dispensing and removal station.  
         [0022]    [0022]FIGS. 10A and 10B are side cross sectional views of a vacuum hose and transport mechanism for removing liquid reagent and wash fluids from slides contained on the slide rotor.  
         [0023]    [0023]FIG. 11A is a side cross-sectional view of the aspiration head, showing its relationship to the glass slide in the slide frame.  
         [0024]    [0024]FIG. 11B is a bottom en face view of the aspiration head.  
         [0025]    [0025]FIG. 12 is a perspective view of a second embodiment of a slide stainer.  
         [0026]    [0026]FIG. 13 is a perspective view of the liquid handling zone of the second embodiment of the slide stainer.  
         [0027]    [0027]FIGS. 14A and 14B are side cross-sectional views of the liquid aspiration station of the second embodiment, with the aspiration head in the lowered (FIG. 14A) and raised (FIG. 14B) positions.  
         [0028]    [0028]FIG. 15 is a schematic representation of the waste liquid pathways of the second embodiment.  
         [0029]    [0029]FIG. 16 is a schematic representation of the bulk liquid dispense pathways of the second embodiment.  
         [0030]    [0030]FIG. 17 is a schematic representation of the individual heaters on the slide rotor and the temperature control boards mounted on the slide rotor.  
         [0031]    FIGS.  18 A-D are a schematic diagram of the electronic circuitry of the temperature control board. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    [0032]FIG. 1 shows a first embodiment 1 of the invention in perspective view. Generally, the first embodiment 1 comprises a substantially circular assembly base  2 , a slide rotor  3  rotatable on the assembly base  2 , a reagent rotor  4  also rotatable on the assembly base, and a liquid dispensing and removal station  5 .  
         [0033]    The slide rotor  3  is driven to rotate by a servo motor (not shown) and carries ten slide frames  6  that are radially asserted into and detachable from it. A top view of single slide frame  6  is shown in FIG. 2. Here, positions for five slides, each with a tissue sample, are shown in positions  7   a - 7   e.  The slide frame  6  comprises a slide frame base  8  shown in FIG. 3. The slide frame base  8  includes a heated area  9  which underlies each of the slide positions  7   a - 7   e  and incorporates resistive heating elements, not shown. The heating elements are integrally formed in the slide frame base  8 . Electricity for powering the heating elements is provided into the slide frame  6  from the assembly base  2  via first and second contacts  10 . Further, third and fourth contacts  11  enable temperature sensing of the heated areas via thermocouples also integrally formed in the slide frame base  8 . In practice, a sum of three connectors are required, since contacts  10  and  11  share the same ground connection. Therefore, one of the connectors  11  are left unused.  
         [0034]    Adapted to overlay the slide frame base is a slide frame housing  12 . FIG. 4 is a top view of the slide frame housing  12  showing essentially a rigid plastic or metal frame  13  with five oval holes  14   a - 14   e  corresponding to each of the slide positions  7   a - 7   e.  A silicon rubber gasket  15  is also provided under the frame  13 . Returning to FIG. 2, the slide frame housing  12 , including the gasket  15  and frame  13 , is bolted onto the slide frame base  8  by two Allen bolts  16  to provide individual sealed cavities approximately 0.2-0.4 inches deep over each tissue sample slide placed at each of the slide positions  7   a - 7   e.  As a result, a total of 3 ml of reagents and/or rinses can be placed in contact with the tissue samples of each one of the slides but a maximum quantity of 2 ml is preferable. Since the silicon gasket  15  is compressed by the frame  13  against the microscope slides (not shown), the cavities over each of the frame positions are mutually sealed from each other.  
         [0035]    [0035]FIG. 5 is a top view of a slide frame base  8  with five microscope slides  17  in the positions denoted by  7   a - 7   e  in FIG. 3. The area of each slide  17  forming cavities, that are delimited by the silicone rubber gasket  15  and holes  14   a - 14   e  is indicated by an approximately rectangular line  18 , marking the chamber wall. The area denoted by the hatched bars indicates the area of the slide frame base  8  that includes heating elements  9 . The entire heated area (hatched bars) is raised to the same temperature, bringing the group of five slides to the same desired temperature. The portion of each slide  17  that is not above the heated area does not generally bear a biologic tissue specimen. Rather, it is used for labeling purposes.  
         [0036]    [0036]FIG. 6 is a cross-sectional view of an assembled slide frame base  8  and housing  12 , collectively referred to previously as the slide frame  6 . The microscope slide  17  is shown held in position, between the slide frame base  8  and housing  12 . The slide frame  6  is resting on the slide rotor  3 . In this view, the electrical connection between the slide frame  6  and an edge connector  19  is demonstrated. Four edge connectors per slide frame  6  are provided (contacts  10  and  11  in FIGS. 2 and 3). The electrical connection is fed from the edge connector  19  through the slide rotor via an insulated feed-through  20 , to a terminal underneath the slide rotor  3 . A wire then connects the terminal to a source of power or control circuitry (not shown).  
         [0037]    [0037]FIG. 7 is a schematic diagram, showing two out of the ten heater  91  and sensor  92  circuits that can be placed on the instrument slide rotor. The heater is represented schematically as a resistive element, and corresponds to the heated area (hatched bars) of FIG. 5. Contacts  10  and  11  share a common ground connection, leaving one of the four connectors unused. Each of the circuits feeds into a temperature controller, represented schematically  21 . Each slide frame sends three wires to the temperature controller  21 —a heater power conductor  22 , a sensor conductor  23 , and a ground connection  24 . The temperature controller  21  is mounted in a stationary position on the assembly base  2 . Since the heaters and sensors are in frequent motion, they connect to the stationary temperature controller  21  via a service loop (not shown). The service loop contains the wires from each of the edge connectors  19 . Sufficient extra length is provided in the wires so that as the slide rotor rotates, the service loop travels around the slide rotor axis. The slide rotor  3  does not turn more than one full revolution in either direction. The wires in the service loop are preferably bundled together with a wire tie, so that individual wires do not become entangled or caught underneath the slide rotor  3 . Since there are three wires per circuit (wires  22 - 24 ), and there are ten slide frames  6  on the slide rotor  3 , the service loop contains a minimum of thirty wires.  
         [0038]    Referring to FIG. 1, positioned above the slide rotor  3  is the reagent rotor  4 . This reagent rotor is similarly adapted to rotate on the assembly base  2  and is driven by another servo motor (not shown) under computer control (not shown). The reagent rotor  4  and the slide rotor  3  rotate independently of each other. The reagent rotor  4  is adapted to carry up to ten cartridge frames  25 . Each of these cartridge frames  25  are detachable from the reagent rotor  4  and can be selectively attached at any one of ten possible points of connection. Each cartridge frame  25  is capable of carrying five of the cartridge pumps  46 .  
         [0039]    Generally, the dispensing station  5  comprises a soft hammer  26  for engaging a portion of the cartridge pumps  46 . The cartridge pumps  46  are constructed so as to dispense liquid when a portion of the cartridge pump  46 , called the metering chamber  42  of the cartridge pump  46  is compressed. It is possible to dispense from any of a plurality of cartridge pumps by rotating the reagent rotor so as to align a desired cartridge pump  46  with the hammer  26 . This provides the capability of dispensing precisely measured amounts of reagent to any slide positioned underneath the cartridge pump  46  adjacent to actuator  26 . The mechanism for dispensing from the cartridge pumps  46  is shown in greater detail in FIG. 8. The hammer  26  is driven by a solenoid or linear stepping motor  43  that is mounted on a front wall  44 , attached to the assembly base  2 . In FIG. 8, the hammer is shown compressing the metering chamber  42  portion of the cartridge pump. It is important to be able to adjust the speed of compression by the hammer  26  upon the metering chamber  42 . Otherwise, too rapid a compression will cause an excessively forceful ejection of reagent from metering chamber  42 , potentially damaging the tissue section underneath. Therefore, a linear stepping motor is preferred instead of a solenoid. As another alternative, the reciprocating hammer of the dispensing actuator could take the form of a cam, driven by a rotary motor, that engages the metering chamber  42  so that the rotation of the cam will compress the metering chamber.  
         [0040]    The cartridge pump  46  is comprised of a liquid reservoir  45  and the metering chamber  42 . The liquid reservoir  45  shown in this first embodiment 1 is a syringe barrel. The metering chamber  42  is comprised of a compressible elastomeric housing with a one-way inlet valve (not shown) and a one-way outlet valve (not shown), both valves aligned in a downwards direction of fluid flow. When the hammer  26  compresses the metering chamber  42 , the liquid reagent contained within is ejected. When the compressive force is removed, the negative pressure created by the expansion of the elastomeric housing, trying to resume its native, non-compressed shape, causes liquid to flow inwards from the liquid reservoir  45 . In this manner, repetitive compression of the metering chamber  42  causes repetitive dispensing of small aliquots of reagent. Alternative cartridge pumps are presented in U.S. patent application Ser. No. 08/887,178 filed Jul. 2, 1997 and U.S. patent application Ser. No. 09/020,983 filed Feb. 10, 1998 which are incorporated herein by reference.  
         [0041]    The dispensing station  5  further includes a means to dispense liquids from a large bottle (FIG. 9). Bulk liquid bottles  27  that can supply liquid into any one of the microscope slides  17  on any one of the slide frames  6  via rinse tubes  28 . Each bulk liquid bottle  27  is connected to its own rinse tube  28 . The bulk liquid bottles  27  are pressurized by a pump (not shown). The outflow tube (not shown) from each bulk liquid bottle  27  passes through a valve  47  that regulates the flow of liquid from that bottle. By opening the valve for a defined period of time, under computer control (not shown), with a defined pressure within the bottle  27 , a known quantity of liquid can be dispensed onto the slide  17 . The liquids placed within the bottles  27  are those that are used repeatedly among many different procedures, such as water, saline, and alcohol.  
         [0042]    As shown in FIG. 9, the bulk liquid bottles  27  are screwed into a female threaded cap  48  secured to the underside of the horizontal top wall  49  of the station frame. Compressed air from a compressor (not shown) is provided to each bulk liquid bottle  27  through a pressure regulator  50 . Tubing from the pressure regulator  51  transmits the compressed air to the inlet of the bulk liquid bottle  27 . The pressure above the liquid enables the liquid to forced up through the dip tube  52  through the rinse hose  53  when a pinch valve  47  is opened. Depending on the length of time that the pinch valve is opened, a pre-determined amount of liquid can be dispensed through the rinse tube  28 .  
         [0043]    The liquid dispensing and removal assembly  5  further includes a liquid removal vacuum station, positioned adjacent to the rinse tubes  28  (not visible in FIG. 1). In order to remove liquid from the surface of a slide  17 , the reagent rotor positions the slide at the liquid removal vacuum station, shown in a side cross-sectional representation in FIGS. 10A and 10B. An external source of vacuum (not shown) is channeled through a trap flask  29 , ultimately leading to a vacuum hose  30  that terminates in an aspiration head  31 . The tubing connections are not shown in FIGS. 10A and 10B. The vacuum hose  30  and aspiration head  31  are supported by a hose transport mechanism  54  that allows the aspiration head  31  to be extended down into a cavity of a slide frame  6  to remove liquid covering the tissue sample on the slide  17 . As the aspiration head contacts the liquid, the liquid is sucked upwards into the tubing and collected into the trap flask  29 .  
         [0044]    The vacuum hose transport mechanism  54  comprises a motor  32 . A reciprocating link  33  is attached to a crank arm  34  so that the rotation of the motor  32  causes the reciprocating link  33  to traverse in a vertical direction. A bottom portion of the reciprocating link  33  is connected to a lever  55  that is pivotally attached to the station frame. The other end of this lever is connected to a vacuum hose clamp  35  that is connected via pivot arms  36  to a plate  37  rigidly attached to the station frame. The net effect of these connections is that when the motor  32  is rotated, the slide arm  33  descends in a vertical direction. Thus, the lever  55  is pivoted clockwise around its fulcrum causing the hose clamp  35  to pivot up and away on the two pivot arms  36  from the slide as shown in FIG. 10B. The motor is automatically turned off as the link  33  reaches its two extreme ends of movement by the contact of the electrical terminals  39  of the link to the contact plates  38  connected to the station frame.  
         [0045]    The aspiration head  31  is shown in greater detail in FIGS. 11A and 11B. FIG. 11A shows the aspiration head in a lowered position, in cross-section, within the cavity formed by the slide frame  6 . The aspiration head  31  comprises a hollow interior manifold  40  through which the vacuum force is transmitted across the entire lower surface of the aspiration head  31 . Eight holes  41  are drilled on the lower face of the aspiration head  31 , through which the suction force is transmitted. Since the microscope slide  17  is planar, liquid on the slide surface spreads out in two dimensions. Therefore, in order to thoroughly remove liquid from all portions of the microscope slide  17 , multiple aspiration sites are needed. We accomplish this with an aspiration head with a planar lower surface with multiple holes. The planar surface of the aspiration head  31  comes into close parallel apposition to the microscope slide  17 . The aspiration head only contacts the liquid, not the microscope slide itself, lest it damage the glass slide  17  or the biologic specimen that it carries (not shown). Without such a design and only a single aspiration site, such as from a pipette, liquid distant from the aspirator would not be removed. Rather, it would cling to the distant surfaces of the glass slide  17 , because of the surface tension on the glass. This would result in a residual volume of liquid that would otherwise be left on the surface of the slide  17 . Having a close parallel apposition of the aspiration head is also helpful from the perspective of decreasing surface tension during liquid aspiration. The close parallel apposition of the bottom surface of the aspiration head with the microscope slide  17  creates a type of capillary gap. This gap helps to overcome surface tension, ensuring complete liquid removal.  
         [0046]    A computer, not shown, controls the instrument functions. That is, an operator programs the computer with the information such as the location of reagents on the reagent rotor and the location of slides on the slide rotor. The operator then programs the particular histochemical protocol to be performed on the tissue samples. Variables in these protocols can include the particular reagent used on the tissue sample, the time that the tissue sample is allowed to react with the reagent, whether the tissue sample is then heated, the rinse that is then used to wash the reagent away, followed by the subsequent removal of the rinse and reagent to allow subsequent exposure to a possibly different reagent. The instrument enables complete random access, i.e., any reagent to any slide in any sequence.  
         [0047]    A second, preferred, embodiment of the invention is shown in FIG. 12. Like the previous embodiment, it also comprises two independent carousels that rotate on an assembly base  56 . Bulk liquid bottles  57  are mounted on a bridge  58  that extends across the width of the entire machine, above the reagent rotor. A separate group of trap bottles  59 , for collecting waste liquid, are mounted on the side of the bridge  58  in a compartmentalized shelf. The tubing connections and valves for the bulk liquid bottles  57  and the trap bottles  59  are hidden from view by an upper panel  60 . The front and sides of this embodiment are surrounded by a plexiglass case  61 , that can be manually slid sideways in order to insert cartridge pumps  62  or slides (not shown). Slides are individually inserted and removed via a centrally located slide access door  63 . The slides (not shown) are hidden from view by a circular platen  64  that is located above the slides and reagent rotor (not shown). Functions similar to the dispensing assembly ( 5  of FIG. 1) in the previous embodiment are accomplished in a somewhat similar liquid handling assembly (not shown) that is positioned in a liquid handling zone  65 .  
         [0048]    [0048]FIG. 13 shows the individual mechanisms contained within the liquid handling zone  65 , including a hammer  66  for dispensing from cartridge pumps (not shown), an aspiration head  67  for removing liquid from the surface of slides, a bulk liquid dispensing port  68 , and an air-mix head  69  for spreading and mixing liquids on the surface of a slide. The electromechanical mechanism for dispensing from cartridge pumps, by compressing a hammer  66  upon a metering chamber of a cartridge pump (not shown in FIG. 13), is similar to the previous embodiment (FIG. 8). Reagent dispensed from the cartridge pump (not shown) flows onto the slide by passing through a roughly rectangular hole in the platen  64 .  
         [0049]    The aspiration head  67  also functions in a similar manner to that of the previous embodiment. In order to simplify the linkage mechanism for lowering and raising the head  67 , the head moves solely in a vertical direction. This is shown in further detail in FIGS. 14A and 14B. FIG. 14A shows a side cross-sectional view of the aspiration head in a down position, within a cavity formed by the microscope slide  75  (bottom surface) and a slide chamber clip  76  (lateral walls). As in the first embodiment, a gasket (not shown) seals the surface where the slide chamber clip  76  contacts the microscope slide  75 . A linear stepper motor  73  moves the aspiration head up and down, under computer control (demonstrated schematically in FIG. 15). As in the first embodiment  1 , the aspiration head  67  comprises a hollow manifold  74  connected to a source of vacuum. Eight holes communicate between the bottom of the aspiration head  67  and the exterior, through which liquid is aspirated. When vacuum is supplied to the aspiration head  67 , and the head  67  is lowered adjacent to the slide, the liquid reagent on top of the slide is aspirated off and collected in a trap bottle  59  (shown schematically in FIG. 15). When the aspiration head  67  is not in use, it is raised to the up position (FIG. 14B), allowing free rotation of the slide rotor  77 .  
         [0050]    [0050]FIGS. 14A and 14B also show the physical location of a heating element  78 , represented as a resistive element inside a rectangular box with cross-hatched lines. Each slide rests directly on the heating element  78 , so that heat is directly communicated to the microscope slide. A thermistor is incorporated into each heating element (not shown in FIGS. 14A and 14B). Each of forty-nine microscope slides  75  has its own heating element  78 , so that the temperature of each slide  75  can be independently regulated. Power for the heating element  78  is supplied directly from a temperature control board  79  that is affixed to the underside of the slide rotor  77 . Seven identical temperature control boards  79  are so mounted underneath the slide rotor  77 , evenly spaced around the periphery. Each temperature control board supplies power for seven heating elements  78 . The means by which this is accomplished is explained later, in reference to FIGS. 17 and 18A-D.  
         [0051]    An important aspect of this embodiment, not highlighted in the previous embodiment  1 , is the provision for the segregation of waste liquids that are removed from the surface of the slide. A schematic diagram explaining how this is accomplished is shown in FIG. 15. Three different waste bottles  59  are mounted on the instrument. Connections  70  are also provided on the instrument for a large external trap bottle  71 , typically of a ten or twenty liter capacity for aqueous waste. Four solenoid valves, labelled  80 A- 80 D control to which bottle aspirated liquid will be directed. These valves are under computer control, schematically represented by the box labelled “controller”  86 . Valve  81  is a three way valve. It can allow a direct connection between the vacuum pump  82  and the overflow trap  83 , or between the pump and the ambient environment. A connection to the ambient environment is required if the aspiration system needs to be bypassed when the air-mix head  69  is in use. If valves  80 A and  81  are appropriately opened, the pump  82  turned on, and the aspirator head  67  lowered so as to aspirate liquid, the liquid will be directed upwards into the tubing, as represented by the arrow “fluid flow.” Liquid will then follow the only path available, and be collected into the external trap bottle  71 . Valves  80 B- 80 D function similarly for their respective trap bottles  59 . A small overflow trap bottle  83  is also inserted into the line with its own fluid sensor  93 . This provision is included so as to detect if any of the trap bottles  59 , or external trap bottle  71  are overflowing with waste liquid. In that case, liquid would enter the overflow trap bottle and be detected by the fluid sensor. That information would be communicated to the controller  86 , which would shut the system down and alert the instrument operator on the computer screen.  
         [0052]    Referring to FIG. 13, the liquid handling zone also includes an air-mix head  69 . A schematic representation of the air flow into the air-mix head  69  is shown in FIG. 15. The pump generates a high velocity air stream that is channeled into the air-mix head  69 . Air intake to the pump is via the three way solenoid valve  81  (FIG. 15). The solenoid valve  81  (FIG. 15) switches so as to channel air directly from the atmosphere to the pump (FIG. 15), bypassing the aspiration system and trap bottles  59  and  71 . The high velocity air flow is focused onto the slide. The air-mix head  69  travels back and forth along the length of the slide, pushed and pulled by a belt and pulley that is attached to a motor (not shown). The net effect of this system is to direct a curtain of air back and forth along the length of the slide, causing liquid to be mixed and spread along the surface of the microscope slide.  
         [0053]    The liquid handling zone  65  (FIG. 12) includes a bulk liquid dispensing port  68  (FIG. 13). The function of the rinse tubes  28  of the first embodiment 1 (shown in FIG. 1) are all incorporated into a single bulk liquid dispensing port  68  in this preferred embodiment. Therefore, slides are positioned under the bulk liquid dispensing port  68  regardless of the bulk liquid bottle that the liquid is actually derived from. A schematic representation of the fluid pathways and control valves is shown in FIG. 16. The bulk liquid bottles  57  are each connected to a source of pressure, that is generated by a pump  85 . The pressure is communicated to the bulk liquid bottles  57  via a pressure manifold  94 . Solenoid valves  72   a - 72   f  are placed between the bulk liquid dispensing port  68  and each bulk liquid bottle  57 . Liquid flows out the bulk liquid dispensing port  68  only when one or more of the valves  72   a - 72   f  are open. A pressure switch  84  also communicates with the pressure manifold  94 . It is capable of sensing the amount or pressure contained within the manifold  94 . When it falls below a specified level, it communicates with the controller  86  causing activation of the pump  85 . As the pump generates an increased amount of air pressure within the pressure manifold, the pressure switch resets, causing the pump to stop pumping. In this manner, a relatively constant pressure head is maintained within the pressure manifold  94 .  
         [0054]    A dispense sensor  95  is positioned underneath the bulk liquid dispensing port  68  to provide verification that liquid was dispensed when one of the solenoid valves  72   a - 72   f  were transiently opened. The dispense sensor  95  comprises an optical sensor and an LED light source. When liquid is dispensed from the bulk liquid dispensing port  68 , the liquid interrupts the light beam. The change in resistance across the sensor as a result of the decrement in light intensity is communicated to the controller  86 .  
         [0055]    This second, preferred embodiment of the invention includes the capability to independently heat the forty-nine slides to different temperatures. A novel aspect of this embodiment is the method for independently regulating the amount of power that each of the forty-nine heaters receives. Moreover, each heater also incorporates a temperature sensor. Each of these sensors must communicate with the computer  86  in order to allow for appropriate temperature feedback and regulation. In the first embodiment 1, groups of up to five slides were under a single, common temperature control mechanism. Each heating group had wires that directly connected with the temperature controller (FIG. 7). With three wires per group (power for heat, sensor feedback, and a shared ground) and ten groups of slides, at least thirty wires were contained in the service loop. If a similar system were used for forty-nine different heaters, as in this preferred embodiment, 147 wires would be required in the service loop. Such a bulky service loop would be problematic. Therefore, an alternative method is developed in this preferred embodiment.  
         [0056]    [0056]FIG. 17 shows the relationship between each of the heating elements  78  mounted on the slide rotor  77 , depicting the heating element  78  as a resistive element. A single sensor  87  is adjacent to each heater. The combination of a single heating element  78  and sensor  87  are so positioned so as to provide a location  88  for a single slide to be heated. The physical layout of this location  88  is demonstrated in FIGS. 14A and 14B. Two wire leads from each heating element  78 , and two wire leads from each sensor  87  are connected directly to a temperature control board mounted on the slide rotor  77 . Each temperature control board is capable of connecting to up to eight different heater and sensor pairs. Since this embodiment incorporates forty-nine slide positions, seven boards  79  are mounted to the underside of the slide rotor, each connecting to seven heater-sensor pairs. One heater-sensor position per temperature controller board  79  is not used. Also shown in FIG. 17 is the serial connection  89  of each of the seven temperature control boards, in a daisy-chain configuration, by six wires. The first temperature control board is connected via a service loop  90  to the computer  86 . The service loop contains only six wires tied together in a harness.  
         [0057]    FIGS.  18 A-D are an electronic schematic diagram of the temperature control board  79 . The design of the temperature control board  79  was driven by the need to minimize the number of wires in the flexible cable (service loop  90 ) between the heaters and the computer. To minimize the length of wires, seven temperature controller boards  79  are used, each mounted on the slide rotor. Thus, each heater is positioned close to its associated electronics and the size of each board  79  is kept small because each runs only seven heating elements  78 . Each temperature controller board  79  includes the function of an encoder and decoder of temperature data. That data relates to the actual and desired temperature of each of heating elements  78 . The data flows back and forth between the computer  86  and the temperature control board  79 . If an individual heating element  79  requires more or less heat, the computer communicates that information to the temperature control board  79 . The temperature control board  79 , in turn, directly regulates the amount of power flowing to each heater. By placing some of the logic circuitry on the slide rotor, in the form of the temperature control boards  79 , the number of wires in the service loop  90 , and their length, are minimized.  
         [0058]    In this embodiment, the temperature control board  79  system was designed as a shift register. The machine&#39;s controlling microprocessor places bits of data one at a time on a transmission line, and toggles a clock line for each bit. This causes data to be sent through two shift register chips on each control board, each taking eight bits. There are thus 16×7 or 112 bits to be sent out. Referring to FIGS.  18 A-D, the data comes in on connector J 9 . 1 , and the clock line is J 9 . 2 . The shift registers used in this design are “double buffered,” which means that the output data will not change until there is a transition on a second clock (R clock), which comes in on pin J 9 . 3 . The two clocks are sent to all seven boards in parallel, while the data passes through the shift register chips (U 1  and U 2 ) on each board and is sent on from the second shift register&#39;s “serial out” pin SDOUT to the input pin of the next board in daisy chain fashion. It will be seen that a matching connector, J 10 , is wired in parallel with J 9  with the exception of pin  1 . J 10  is the “output” connector, which attaches via a short cable to J 9  of the next board in line, for a total of seven boards. The other three pins of J 9  are used for power to run the electronics (J 9 . 4 ), electronic ground (J 9 . 5 ), and a common return line (J 9 . 6 ) for temperature measurement function from the sensors.  
         [0059]    Of the sixteen data bits sent to each board, eight control the on/off status of up to eight heating elements  78  directly. This can be accomplished with a single chip because shift register U 2  has internal power transistors driving its output pins, each capable of controlling high power loads directly. Four of the remaining eight bits are unused. The other four bits are used to select one thermistor  87  out of the machine&#39;s total complement of forty-nine. For reasons of economy and to reduce the amount of wiring, the instrument has only one analog-to-digital converter for reading the forty-nine temperature transducers (thermistors  87 ), and only one wire carrying data to that converter. This channel must therefore be shared between all of the transducers (thermistors  87 ), with the output of one of them being selected at a time. Component U 4  is an analog multiplexer which performs this function. Of the four digital bits which are received serially, one is used to enable U 4 , and the other three are used to select one of the component&#39;s eight channels (of which only seven are used). If pin four is driven low, U 4  for that board  79  becomes active and places the voltage from one of the seven channels of that board on the shared output line at J 9 . 6 . Conversely, if pin four is pulled high, U 4 &#39;s output remains in a high impedance state and the output line is not driven. This allows data from a selected board  79  to be read, with the remaining boards  79  having no effect on the signal. Multiplexer U 4  can only be enabled on one board  79  at a time; if more than one were turned on at a time, the signals would conflict and no useful data would be transmitted.  
         [0060]    Temperature sensing is accomplished by a voltage divider technique. A thermistor  87  and a fixed resistor (5.6 kilohms, R 1 -R 8 , contained in RS 1 ) are placed in series across the 5 volt electronic power supply. When the thermistor is heated, its resistance drops and the voltage at the junction point with the 5.6 kilohm resistor will drop.  
         [0061]    There are several advantages to the design used in this embodiment. Namely, the temperature control boards  79  are small and inexpensive. Moreover, the heater boards are all identical. No “address” needs to be set for each board  79 . Lastly, the service loop  90  is small in size.  
         [0062]    An alternative potential design is that each temperature control board  79  could be set up with a permanent “address” formed by adding jumper wires or traces cut on the board. The processor would send out a packet of data which would contain an address segment and a data segment, and the data would be loaded to the board whose address matched the address sent out. This approach takes less time to send data to a particular board, but the address comparison takes extra hardware. It also demands extra service loop wires to carry the data (if sent in parallel) or an extra shift register chip if the address is sent serially. As yet another potential design is that each temperature control board  79  could have its own microprocessor. They could all be connected via a serial data link to the main computer  86 . This approach uses even fewer connecting wires than the present embodiment, but the cost of hardware is high. It also still implies an addressing scheme, meaning that the boards would not be identical. Also, code for the microprocessors would be required.  
       Equivalents  
       [0063]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described specifically herein. Such equivalents are intended to be encompassed in the scope of the claims.  
         [0064]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.