US 3903908 A
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Description (OCR text may contain errors)
United States Patent 11 1 Logue et a1.
[ SLIDE STAINING APPARATUS  Inventors: John Logue, Pangbourne; Michael J.
Coulson, Stokenchurch, both of England  Assignee: Columbia Industrial Developments Limited, Slough, England  Filed: Oct. 31, 1973  Appl. No: 411,586
[4 1 Sept. 9, 1975 3,674,040 7/1972 Howells et a1. 134/76 3,691,988 9/1972 Clarke 3,731,648 5/1973 Gerber et a1 118/6  ABSTRACT A device having two cooperating traversing means to move a carrier to any of a selected number of predetermined positions above treatment solutions and lower one or more specimens into the treatment solutions for a selected period of time with a control permitting selection of the sequence of treatments as well as the duration of treatments and capable of directing drive systems to proceed through each of the selected sequence steps automatically. Preferably, the treating solutions are arranged orthagonally and carried in a sliding tray which may be extended from the cabinet for replenishment or replacement. One particular advantage of the system is the location of the mechanical mechanism and electrical components above the solutions which avoids damage from dripping and spillage.
4 Claims, 7 Drawing Figures PATENTEDSEP ems 3.903.908
SliEET 1 BF 5 PATENTED SEP 9 I975 sum 3 BF 5 IMEKQU PATENTEDSEP 9875 3,903,908
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RRI$E=Z H I2 I3 M- Y posmorv x POSITION MINUTES secowvs x10 PROCESS STAGE 2 X X X PROCESS STAGE 3 2 FIG. 5B
SLIDE STAIN [NG APPARATUS This invention relates to apparatus for automatically treating an article at a succession of processing stations and is particularly, though not exclusively, concerned with automatic slide staining apparatus where the article to be treated comprises a slide or a batch of slides.
Slide staining is required in numerous medical fields such as for example histology, cytology and haematology. Usually, a batch of slides to be stained requires treatment successively with several different reagents for various lengths of time so that the slides can be properly stained. As a result of high work loads in medical laboratories and a shortage of trained technicians, automatic slide staining apparatus was introduced to reduce both the manual supervision required and the risk of human error in a complicated staining routine.
One known type of automatic slide stainer has a series of reagent baths arranged along the predetermined fixed travel path of a motor driven jib which supports a carrier for a batch of slides, the jib being arranged to move along its travel path and dunk the slides into one bath after another in succession. A rotary arrangement is known in which the travel path of the jib is circular and also a rectilinear arrangement is known (see for example US. Pat. specification No. 2,853,084). The dwell times of the jib at the reagent bath positions and correspondingly the slide immersion periods are determined by a timing device which commonly includes a constantly driven rotating circular timing card whose edge is notched at intervals. A timing clock control lever engages the notches consecutively as the card rotates and the times the slides spend in the reagent baths are determined by the spacings between the notches.
Besides being very bulky and thus inconvenient for use where space is restricted and also being constructed such that in operation it is not possible easily to gain access to or to inspect the reagent baths, the above type of automatic stainer has proved to have other disadvantages as the demand for slide staining has increased, in particular the demand for Papaniculaou staining for cervical smearsv In view of diffiuclties which arise in altering a staining programme, it is usual to program the stainer to operate in accordance with a multipurpose routine applicable to a number of different types of slide even though for any particular type of slide, it would be possible to greatly shorten the staining operation by modifying the programme. These difficulties arise since, firstly, if it is required to alter the sequence of dunking in the reagent baths, it is necessary to change the positions of the reagent baths relative to each other. This may be undesirable where noxious fumes are produced, and there is also the risk of spillage of the reagents from the baths or inadvertent misplaccment of baths during a changeover operation. Secondly, the notching of the timing card is a timeconsuming operation and there is a substantial risk of notching the card incorrectly.
According to one aspect of the present invention, there is provided apparatus for automatically and successively positioning an article at selected stations of a number of available processing stations, said apparatus including a movable carrier for said article, drive means coupled to said carrier for direct movement of an article therein to any of said processing stations from any other station. and control means for determining the operation of said drive means, the control means including means programmable for selecting the stations to be visited by the carrier and for defining the sequence in which the selected stations will be visited in operation of the apparatus.
By virtue of the provision of programmable drive control means it is possible to readily alter the stations visited and the sequence in which stations are visited in operation of the apparatus and thus, when the invention is incorporated in an automatic slide stainer, it is possible to alter the program of the dunking of the slides in the reagent baths without altering the positions of the baths themselves.
In order to reduce the time for movement of an article between successive stations in a routine, the drive means and control means are preferably arranged so that the article is movable directly between any of the available processing stations and any other station, and not for example so that the article is movable only along a fixed path between the available positions, since in this latter arrangement it might be necessary for the article to make several circuits of the available positions during the performance of a processing routine.
The programmable means for determining the station selection ans station visiting sequence of the apparatus preferably includes an electrical plugboard having a series of groups of positions into which plugs may be inserted, each group corresponding to one stage in a processing routine and the plugs inserted in a plug group position determining a processing station to be visited and preferably also the dwell time of an article in the processing station. In operation of the apparatus the groups are read" in turn and the station to be visited in each processing stage is determined by the plugs inserted in the respective group of plug positions. Preferably, the plugs are internally constructed in several different ways so that the insertion of different plug types into the same group of plug positions defines different processing stations to be visited. For example, different types of plugs may contain resistors of different values so that, when the plug group position is read, the magnitude of an output signal on an output line leading from the plug group position is dependent on the types of plugs inserted therein. Alternatively and as preferred, the plugs may contain one or more diodes arranged so that, when a plug is inserted in a plug position, each diode is coupled to one of a plurality of output lines leading from the plug position thereby to pro vide a binary coded signal on the output lines when the plug position is read. One advantage of such an arrangement is that inexpensive 1C logic circuitry may be used to process the output signal.
The utilization of plugboard programming affords great simplicity in altering a programme and besides this, a further advantage of employing plugboard programming is that the programme can be readily inspected by noting the positions of the plugs in the board. Different types of plugs can be marked distinctively so that the processing station to be occupied by an article at each stage of a process can be noted at a glance.
In a preferred and particularly convenient embodiment of the invention, the stations which are available to be visited by an article are arranged in a grid. Such an arrangement in a slide stainer enables the reagent baths to be arranged compactly thereby enabling the overall size of the apparatus to be reduced. Furthermore. such an arrangement enables the drive and control means to be separated into two parts, one part regulating movement parallel to a first axis of the grid and the other part regulating movement parallel to the second axis of the grid. This is particularly convenient where plugboard programming is employed since in each group of plug positions, one or more plug positions may be assigned to programme the position of a processing station relative to the first axis of the grid, and one or more other plug positions assigned to programme the position of the station relative to the second axis. As mentioned previously herein the dwell time spent by an article in each station of a processing routine is conveniently determined also by plugs inserted in the plugboard. This again lends itself to ease of variation of the processing routine, and avoids the disadvantages noted above of the mechanical timing device which requires performance of the time consuming operation of notching a card.
This gives rise to a further aspect of the invention whereby there is provided apparatus for automatically and successively positioning an article at selected stations of a number of available processing stations arranged in a grid, said apparatus including a moveable carrier for said article, first and second drive means coupled to said carrier for movement thereof in first and second directions parallel to the axis of the said grid whereby the carrier is moveable between any of the said processing stations, and control means for determining the operation of the said first and second drive means, the control means including an electrical plugboard having a plurality of groups of plug positions, each group relating to one stage of a processing routine and having plug positions connected to receive plugs indicative of station address coordinates in the grid for controlling separately the movements of said first and second drive means and one or more plug positions connected to timing control means to receive one or more plugs indicative of in-station dwell time, means for scanning said groups of plug positions sequentially to read the information provided by plugs received therein, and means responsive to the information read from said groups for providing command signals to said first and second drive means.
Preferably, the timing control means is arranged so that if no plugs have been inserted in the one or more timing plug positions of a group and yet station address plugs have been inserted, the article is held in the addressed processing station for a predetermined minimum time period. In a slide stainer, this predetermined minimum time period can be the minimum time required merely to insert ansd promptly extract a batch of slides from a reagent bath without allowing any finite immersion period. This facility is useful in some staining routines and is an advantage which is not shared by the known slide stainer described above where it is not possible to notch the card closely enough and accurately enough to provide very short and accurate periods of slide immersion.
The control means preferably includes a central sequence counter the function of which is to regulate the operation of the apparatus during each stage of a processing routine and, when a stage is completed, to initiate the next stage of the routine.
During each processing stage, the sequence counter is adapted to send command signals in sequence to the other parts of the apparatus, and, where appropriate, requires the reception 0 command obeyed" signals before the next command signal can be transmitted. The sequence counter is preferably arranged to transmit command signals simultaneously to the said first and second drive means so that the two drive means can be activated simultaneously in order to give a fast diagonal movement of the carrier across the grid between successive processing stations of a processing routine.
The control means preferably also includes means for comparing the next addressed station of a processing routine with the station actually occupied by the carrier in order to derive a signal for instructing the drive means to move the carrier in the appropriate directions. The same analyzer means may also be used for making a check to ensure that a processing stage is not carried out with the carrier out of its addressed station. For determining the actual carrier location in the grid, it is convenient to employ an opto-electronic sensor arrangement responsive to the condition of the carrier drive means.
The apparatus may further include means for effecting desired processing stages at the various processing stations; in the case of a slide stainer, this will comprise means operable when the carrier moves to an addressed processing station for immersing the slides in the reagent bath.
A preferred embodiment of the invention will now be described with refercn cc to the accompanying drawing in which: 1
FIG. 1 is a perspective view of the exterior of an automatic slide stainer according to the invention showing the arrangement of the controls and the reagent baths;
FIG. 2 is a perspective view of the drive arrangement for moving a batch of slides between the reagent baths;
FIG. 3 is a diagrammatic side view in the direction of the arrow 3 of FIG. 2 illustrating part of the drive arrangement;
FIG. 4 is a flow diagram illustrating the sequence of operations carried out in one stage of a processing routine of the slide stainer;
FIG. 5 is a block diagram of the control circuit of the slide stainer;
FIG. 5A is a detailed block diagram of the sequence counter of the control means; and
FIG. 5B is a circuit diagram of part of the plugboard.
Referring to FIG. 1, the preferred embodiment of the device is a slide stainer according to the invention comprising a housing I having a lower compartment la capable of accomodating about 20 reagent baths 2 preferably arranged in a grid, five columns wide by four rows deep. Each column is mounted in a slidable pullout tray 3 supported by base and interlocks with adjacent trays in such a manner that when any one tray is pulled out, for example for changing one or more of its reagent baths, none of the other trays can be pulled out at the same time which minimizes the risk of error when changing reagent baths. As a safety measure, each tray when positioned correctly is arranged to close a switch which when open prevents the slide stainer from operating. A hinged glass cover 4 provides access to the compartment and, when the apparatus is not in use, may be clipped in position over the front of an upper compartment 5 to protect the control panel disposed thereon. The two compartments may be pressurized in use by a fan (not shown) within the apparatus to prevent a hazardous build-up of fumes from the reagents. In addition, a cooling fan (also not shown) may be provided.
Upper compartment 5 contains the remainder of the apparatus. This is a particularly convenient arrangement since it minimizes the bench space required for the apparatus, the amount of bench space needed being determined essentially by the dimensions of the desired size of the beaker grid. Furthermore, this arrangement is advantageous in that it eliminates the risk of spillage of reagent onto moving or electrical parts.
The control panel on the front of the upper compartment comprises control switches 6, a display 7 and a plugboard 8. A compartment 9 houses spare plugs for the plugboard. Switches 6 preferably include a Main on/off switch, a Start Routine" switch and an Interrupt Routine switch which allows the routine to be frozen at any point. The display 7 displays the status in the sequence as each stage is reached in a routine and the time remaining for the completion of the current stage. The plugboard for preseleeting a sequence of movement and immersion times comprises three sets 10 and four columns, 11, 12, 13, 14 of electrical sockets for receiving plugs 15. Eight rows of plug positions are provided in each set of columns, each row forming a group of plug positions and relating to one stage of a routine; a 24 stage routine is thereby possible. The heads of the plugs are marked with a suitable number or letter to identify the position or time which they define. A plug inserted in column 11 defines the grid row or preselected location along the first axis in which the reagent bath for that processing stage is positioned (y position) and plugs inserted in column 12 define the corresponding grid column (x position), or preselected location along the second axis. Plugs inserted in column l3 define the number of minutes the slides are to spend immersed during a routine stage, and plugs in serted in column 14 define the number of tens of seconds. The preselection of movement and immersion times means of the apparatus is arranged such that in a routine the groups of plug positions are read in sequence from top to bottom and from left to right.
Referring now to FIGS. 2 and 3, the drive means and moveable carrier of the slide stainer includes a moveable carrier means mounting a batch of slides in a holder or cage 21, indicated in dotted lines. Carrier 20 is arranged to move the cage in three directions, 2:, y and z and comprises a main body or first traversing means 22 moveable in the .r direction; a lowering means including a jib 23 mounted on body 22 by a vertically slidable frame 24 so as to be moveable in the z direction; and a slide or second traversing means 25, forming the immediate mounting for cage 21, is carried by jib or rail 23 and slidable in the y direction. The mo tion of the cage 21 is regulated by three separate drives: a first motor and drive transmission X20 are arranged to move body 22 in the x direction; a second motor and drive transmission Y20 (see FIG. 3) are arranged to move slide 25 in the y direction on jib or rail 23; and a third motor (not shown for the purposes of clarity) and a drive transmission Z20 of the lowering means are arranged to regulate the raising and lowering of jib 23 and slide 25 with the cage 21 in the z direction.
The .r drive X20 includes a continuously operable reversible electric motor X21 connected through a solenoid operated bidirectional single cycle clutch X22 to a chain drive X23 coupled to carriage body or first traversing means 22 for pulling the carriage along rails X24, mounted in upper compartment 5. In order that the drive may be controlled in accordance with the programme of the slide stainer, it is necessary to compare or locate the actual position of the slides with the desired position as defined by the station address plugs of the preselected movement means in the plugboard so that motor X21 can be instructed to drive in the appropriate forward or reverse direction. The comparing or locating means is described below with reference to FIG. 5: the means for monitoring the position of the slides in the x direction comprises an optical encoder X25 including an apertured disc X26 coupled through a gear train to the drive X23. The disc is apertured with binary coded holes along five equally spaced radii X27 and the gear train is arranged such that each radius X27 occupies a position between a light source X28 and a column of phototransistors X29 when the slides are directly above one of the five reagent bath grid columns. The positions of the apertures in each radius are coded to allow light to fall on selected phototransistors. The output from the phototransistors is a binary coded signal defining the position of the slides in terms of the beaker grid columns.
The y drive Y20 comprises a continuously operable reversible electric motor Y2l connected through a solenoid operated bi-directional single cycle clutch Y22 to a chain drive coupled to slide or second traversing means 25 (see FIG. 3). The chain drive includes a first chain Y23 rotating a shaft Y24 (see FIG. 2) extending parallel to rails X24. A sprocket Y25 mounted on carriage body 22 and keyed for rotation with shaft Y24 and slidable therealong engages a second chain Y26 driving, via suitable free wheeling or pawl devices, slide 25 in either direction along the jib. An optical encoder Y27 for monitoring the Y position of the slide is connected to the chain drive through a gear train. The encoder is identical to that monitoring x movement except in that the disc is apertured along four radii, each radius corresponding to a row of the beaker grid.
It can be seen that slides may be driven in the x and y directions simultaneously, which allows fast diagonal movement of the slides across the grid between processes of a routine.
The 2 drive Z20 of the lowering means comprises a motor (not shown) driving an arm Z21 on which a pulley Z22 is mounted eccentrically. A cable Z23 is fixed at both ends and passes around pulley 222 and pulleys Z24 mounted on carriage body 22 and on vertically slidable frame 23. As shown, the frame 23 and jib 24 are in the raised position. When arm Z21 is rotated by the electric motor through the cable 223 is paid out and allows the jib 23 to drop under its own weight so that cage 22 can be positioned in a reagent bath. In the lowered position of the jib 23, a wheel Z25 mounted on arm Z21 engages a cam Z26 which is continuously rotated by the Z drive motor. The action of the cam Z26 on wheel Z25 imparts a slight rocking movement to arm Z21 and this movement is transmitted via cable Z23 to jib Z4 as an oscillatory movement in the z-plane. This oscillatory movement serves to ensure that reagent is circulated around the slides. The jib is raised by powering the z drive motor to rotate arm 221 through a further 180 to wind in cable Z23.
It is clearly essential that the operation of the x, y and z drives be coordinated in each stage of a routine of slide stainer operation. FIG. 4 is a flow diagram illustrating the sequence of operations carried out in each stage of the routine and in particular shows how the x, y and z drives are coordinated.
Operation 1 involves reading the appropriate plug position group of the plug board to determine the programme for the stage reached in the routine. and entering the time and x, y coordinates into the appropriate parts of the control circuits.
Operation 2 involves determining the actual position of the slides, comparing the slide location with the programmed x, y coordinates and simultaneously instruction the x, y drives to move the slides to the next programmed position. Suitable control circuits are provided to ensure that the jib 23 and slides are raised before the slides are moved across the grid.
in operation 3 the slides are lowered into the chosen liquid reagent bath and when fully lowered, a control timer is started. When the chosen dwell time has been completed, the apparatus moves into operation 4 in which the slides are raised from the beaker. Operation 6 involves indexing the process counter (see below) so that the next plug position group of the plugboard is read when the cycle of operations is repeated in the next stage of the processing.
In the situation where the end of a processing routine is reached, either by reading the last row of the plugboard or by reading a row in which no plugs have been inserted in the station address columns, the cycle of operations is altered in that a process counter (described below) is reset and in operation 2 the slides are moved to a home position on the grid. When operation 2 has been completed an operation 5 occurs in which the timer, for timing the time spent in a process, is reset to allow a new routine to be initiated on receipt of a start routine signal.
FIG. 5 shows the control circuit provided for carrying out the above sequence of operations. A sequence counter, shown in more detail in FIG. 5a, is central to the control circuits. As shown in FIG. 5a the sequence counter comprises a binary counter indexed by a clock and having its output fed to a binaryto-decimal decoder. Outputs from the decoder are connected to various other parts of the control circuit to regulate their operation and provide the above-described cycle of operations. Command obeyed signals derived in the various other parts of the control circuit are supplied to a multiplexer in the overall sequence counter, and the multiplexer functions to gate the binary counter to ensure that command signals are not transmitted from the decoder until the slide stainer has reached the appropriate point in the programmed processing routine.
The sequence counter has a jump control to provide the alternative cycle described above when the processing routine has ended. At such a time, the process counter is reset and an input process counter is gated with a decoder output on line 2 and is connected to the binary counter to cause the count tojump to provide an output signal on decoder line for carrying out operation 5 perviously described.
In considering the operation of the control circuits, it is convenient to start at a point during a processing routine where a command signal has been sent from decoder output line 6 to index the process counter. The output from the process counter is decoded to provide a read signal for the plug group in the plug board defining the next process in the routine. Consider for ex ample that the second plug group is read, i.e. that process 2 of the routine is to be performed. As shown in FIG. 51), for process 2, plugs have been inserted in columns ll, 12, 13 and 14 of the plug board and each plug has one or more diodes coupling the read line to output lines to provide binary coded signals on the output lines. For example, column 11 which provides the station address y-coordinate has inserted therein a plug containing a diode which makes connection to the 1 output line and a diode which makes connection to the 2 output line, which provides on the output lines a binary signal indicating that the slide stainer has been programmed to move the slides to the third beaker grid row. In column 12 which provides the station address .v-coordinate, a plug is inserted which contains a diode arranged to make connection with the iirst output line which is indicative of a station in the first grid column. In column 13, which provides dwell time information in units of one minute, a plug is inserted which contains diodes arranged to make connection with the first and second output lines thus indicating a dwell time of three minutes, and in column 14 which provides additional dwell time information in 10 second units, a plug is inserted which contains a diode arranged to make connection with the third output line which indicates an additional dwell time of 40 seconds. Thus, the coordinates for the processing station in process 2 are (X1, Y3) and the slides have to remain in the reagent for 3 minutes 40 seconds.
A further output from the process counter to display 7 enables the display to indicate the number of the process in the routine.
After the process counter has been indexed, the bi nary counter in the sequence counter is indexed by the clock to provide an output on decoder output line 1 to allow the output signals from the plug board to be entered in the appropriate control circuits. The dwell time signals are entered into a process timer, where they index a counter, and the x and y co-ordinate signals are entered into respective X and Y comparators. Operation 1 is then complete.
The sequence counter is then clocked to provide an output signal on decoder output line 2. This output is fed to the X and Y comparators and enables them to compare the programmed X and y station coordinates with the x and y coordinates of the actual carrier position as determined by the optical encoders X 25 and Y 27. From these comparisons the comparators derive output signals to instruct the motors X 21, l 21 whether to drive forward or to reverse, in order to move the carrier into the programmed station. The output signal from the X and Y comparators are gated by signals from microswitches mounted on the carriage 2l, one of which is closed when the jib 24 is in the raised position (Z top) and the other of which is closed when the jib is in the lowered position (Z bottom). The purpose of this gating is to ensure that the x and y drives operate only when the jib is in the raised position and cannot be operated when the jib is in the lowered position or in some intermediate position. The outputs from the gate circuits provide control signals to the x and y motor controls and to energize the solenoids of the clutches X22 and Y22 so that drive can be transmitted to carriage 21.
The moveable carrier is then moved until the desired position of the lowering means is reached, when the signals from the encoders X25 and Y27 agree with the signals from the plugboard and no further motor drive sigrials derive from the comparators. Operation 2 of the process is then complete and signals are transmitted from the X and Y motor controls to provide an X Y in position" signal at a multiplexer input of the sequence counter which enables the sequence counter to move on to operation 3.
In operation 3, a command signal on decoder output line 3 actuates the Z motor control and enables the Z motor to lower jib 24 and the batch of slides. when the slides have been lowered, a Z bottom" signal is gated with the signal on decoder output line 3 to allow the process timer clock to count down the process timer to zero from the dwell time entered from the plugboard in operation 1. The countdown is displayed on display 7. When the countdown has been completed, the process timer provides a signal T O which gates at G1 the output on decoder output line 3 to prevent any further counting taking place. The signal T also gates at G2 a Z bottom" signal to provide a T 0, Z bottom signal at an input to the multiplexer of the sequence counter to denote that operation 3 has finished and that operation 4 can begin.
Operation 4 involves the raising of the slides by transmitting a signal on decoder output line 4 to the Z motor control. when the jib is raised the top microswitch is closed and a Z top signal is transmitted to an input of the multiplexer so that operation 6, i.e. indexing the process counter as described above, can take place.
Stage 3 of the processing routine is then carried out. it will be noted from FIG. 58 that no plugs have been inserted in columns l3, 14 or row 3. Thus, during stage 3 of the routine, a signal T 0" is provided as soon as the batch of slides is lowered and the apparatus immediately moves on to operation 4, in which the batch of slides is raised, thereby providing a quick dunking" action.
When the processing routine is ended, either by the process counter being fully indexed and returned to zero, or by no plugs having been inserted in the coordinate positions in a plugboard group in which case as described above the process counter is reset to zero, operation 5 is carried out to reset the process timer to allow a new processing routine to be initiated on receipt of a "start" signal at a multiplexer input. A process counter 0" signal is provided at the input to the counter of the sequence counter, and when an output is provided on decoder output line 2, the signal is allowed to pass through the gate to cause the counter to jump to provide an output on decoder output line 5. It will be realized that in the normal course of events where the process counter is not equal to zero, the counter jumps between decoder output 4 and 6. For the sake ot'clarity, the reset control lines have not been indicated in the block diagram.
It will be realized that while the invention has been exemplified with reference to slide staining, it is not limited to this application and could be used, for example, for processing organic tissure preparatory to microsection for pathological study.
What is claimed is:
l. A device for treating a specimen by immersion in a plurality of liquids, which comprises:
a housing having a base,
a series of adjacent trays slideably mounted on said base within said housing so as to be individually moveable into and from said housing.
a plurality of containers for liquids carried on each of said series of said adjacent trays,
moveable carrier means mounted in said housing disposed above said containers,
lowering means moveably disposed on said carrier means adapted to hold said specimen for immersing said specimen in a preselected container,
drive means connected to said carrier means adapted to move said lowering means to a predetermined position above said preselected container,
a first traversing means mounted in said housing and adapted to move along a horizontal first axis,
a second traversing means connected to said first traversing means said second traversing means adapted to move along a horizontal second axis perpendicular to said first axis and to support said lowering means,
timing means responsive to said lowering means for indicating said specimen immersed in said container,
means for determining a preselected sequence of po' sitions along said first axis,
means for determining a preselected sequence of positions along said second axis,
means for determining the location of said lowering means along said first and second axis,
means for counting said preselected sequence of positions along said first and second axis, and
analyzer means responsive to said means for determining a preselected sequence of positions, said location determining means and said means for counting,
control means responsive to said analyzer means connected to said drive means for controlling said drive means to position said lowering means in said preselected sequence,
means for determining a preselected sequence of immersion times, and
control means responsive to said sequence of immer sion times means and timing means connected to said lowering means for controlling the duration of immersion,
whereby a specimen is transported through a presclected sequence of treatments by immersion for an effective time in a plurality of liquids and said low' ering means is moved directly from a position above one preselected container to a position above another preselected container according to the preselected sequence of movement.
2. The device according to claim I wherein said drive means includes:
a first reversible electric motor connected to said first traversing means and adapted to move said first traversing means to predetermined positions along said first axis,
a second reversible electric motor connected to said second traversing means and adapted to move said second traversing means to predetermined positions along said second axis, and
said first and second motors being connected and responsive to said control means responsive to said analyzer means.
3. The device of claim I wherein said means of determining the position of said lowering means along said first and second axes includes:
a first disc connected to said first motor and adapted to rotate responsive to movement of said first trasecond disc connected to said second motor and adapted to rotate responsive to movement of said second traversing means, a coded series of holes in said second disk along a plurality of preselected radii. a light source disposed along one side of said second disc and adapted to illuminate a radially extending elongated area of said second disc, means responsive to light passing through said coded series of holes disposed on the other side of said second disc and adapted to signal the location of said second traversing means in one of said preselected positions along said second axis.
4. The device of claim 1 wherein said housing has a pair of opposed vertical sides,
said carrier means includes a first horizontal track mounted on said sides to support said first traversing means and said first traversing means includes a second horizontal track to support said second traversing means,
interlock means mounted on said housing to prevent withdrawal from said housing of more than one of said trays and switch means to prevent operation of said device when one of said trays is withdrawn from said housing.