Abstract:
An incubator capable of observing an observed specimen in a dish  220  by a microscope while culturing the specimen, wherein light is radiated from a capacitor(C), passed through a hole  273  in a top plate  271 , a hole  275   a  in a upper side plate  275  and a hole  277   a  in a lower side plate  277,  and let into an objective lens (T), and the specimen put in the dish  220  is observed by the microscope, whereby the change of the specimen with elapse of time can be continuously observed or recorded on a videotape while culturing the observed specimen in the dish  220.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to an incubator for observation by microscope. More particularly the invention relates to an incubator capable of observing a specimen while incubating the specimen on the stage of microscope.  
       DESCRIPTION OF THE PRIOR ART  
       [0002]     In the field of biotechnology such as life engineering or biological engineering or pathology, it is necessary to observe though microscope, living specimen such as germs or bacteria with incubating them under controlled atmosphere on which the incubation conditions such as temperature, humidity, or concentration of given gas are maintained for the target specimen.  
         [0003]     In the prior art, specimen are cultured in an container and the container is maintained in an incubator device. When the incubated specimen is observed through microscope, the specimen is picked up and disposed on the stage of the microscope.  
         [0004]     However, there are many disadvantages in such method for observation. In addition that the method requires much labor and it is cumbersome to do it, it is impossible to observe and/or take picture of the specimen as it is being under the incubation conditions. That is, accurate observation cannot be effected since it is conducted under non-controlled conditions.  
         [0005]     In order to solve the problem, the inventor had proposed a temperature-constant, transparent incubator for observation by microscope enabling observation of specimen with incubating on the stage of microscope (see Japanese patent laid open (kokai) public disclosure 10-28576/1998).  
         [0006]     The incubator includes a box-shaped, shallow container of a size just suitable for the stage of microscope. The container also has a hinged lid at one side end, by which the container is opened and/closed. Each of the bottom and the top of the container has a transparent heater plate of glass. The container further comprises an evaporating dish for humidifying and an aperture for delivering carbon dioxide gas into the container.  
         [0007]     In the incubator of such structure, the incubation conditions within the container can be adjusted as desired by humidifying through the evaporation of water contained in the dish, controlling the amount of carbon dioxide gas delivered through the aperture, and raising the temperature controlling the amount of heat generated through the heater plates. The transparent top and bottom plates make it possible to pass light ray therethrough so that specimen such as germs of bacteria being incubated within the container can be observed on the stage of microscope as it is being under the desired incubation conditions.  
       DISCLOSURE OF THE INVENTION However, the above-mentioned incubator of the prior art has following disadvantages.  
       [0008]     (1) It is impossible to use an evaporating dish of large capacity, since a large space within the incubator is already occupied by a sample container such as a dish. In other words, the capacity of the evaporating dish is limited. As a result, when observation is carried out under humidified conditions, the period for which continuous observation can be carried out is limited on the capacity of the evaporating dish. If the incubator is opened to supply water to the dish, the incubation conditions are broken.  
         [0009]     (2) When inserting any tools into the sample container, it is necessary to open the incubator substantially completely. This is because the deep dish-shaped sample container is used. If the incubator is opened completely, the incubation conditions such as the humidity, the temperature, or the concentration of carbon dioxide are broken.  
         [0010]     (3) When observing another portion of the sample put in the container, it is necessary to open the incubator and remove the sample container relative to the objective lens. If the incubator is opened, the incubation conditions are broken.  
         [0011]     (4) As set forth above, if the sample container is put in and out of the incubator, the incubator must be opened. This will lead to breakdown of the incubation conditions.  
         [0012]     (5) When adding drugs or chemicals to the specimen being incubated in the incubator, the incubator must be opened. This will lead to the breakdown of the incubation conditions.  
         [0013]     (6) The more the magnification is increased in microscopic observation; the more the objective lens is to be brought closer to the specimen. In this connection, it is necessary to provide an aperture through the lid (the heater plate) of the incubator to insert the objective lens therethrough. However, it is also necessary to enlarge the diameter of the aperture sufficiently to enable the portion to be observed of the sample varied. Thus, large clearance is to be formed between the edge of the aperture and the objective lens so that the desired incubation conditions cannot be kept within the incubator.  
         [0014]     (7) In the incubator of the prior art, water in the evaporating dish is adapted to be evaporated by the heat energy generated by the transparent conductive film of the thickness of micron order provided on the transparent heater plate of glass, so that generable heat energy may be insufficient to produce water vapor.  
         [0015]     The present invention is provided to solve the above-mentioned problems. It is an object of the invention to provide a new incubator for observation by microscope. In the incubator in accordance with the invention, the incubation and observation of the specimen can be carried out on the stage of microscope, and any operation be carried out to the specimen without spoiling atmosphere generated under set conditions within the incubator.  
       SUMMARY OF THE INVENTION  
       [0016]     These and other objects are achieved by the following incubators for observation by microscope.  
         [0017]     There is provided a fist aspect of a incubator for observation by microscope comprising: an upwardly water tank unit including a container-accommodating portion in which a specimen container such as a dish is to be placed removably at the central portion thereof and a water reservoir disposed around the container-accommodating portion; a lid for covering the upper end of the unit; a heater for heating the specimen container and the unit; and a means for supplying gas into an incubation space defined by the unit and the lid; each of the unit and the lid having at the central portion thereof a light ray transmitting portion for transmitting light ray upwardly or downwardly therethrough.  
         [0018]     There is provided a second aspect of the incubator according to the first aspect  1 , further comprising a means for supplying water into the reservoir from the outside of the unit.  
         [0019]     There is provided a third aspect of the incubator according to the first or second aspect, wherein the heater is of a plate type heating the container from the bottom thereof, and the heater is also provided with a light ray transmitting portion at the position corresponding to those provided on the unit and the lid.  
         [0020]     There is provided a forth aspect of the incubator according to the third aspect, wherein the heater has a laminate comprising upper and lower plates and a heating element interposed therebetween, a top plate disposed above the upper plate with a space from the upper plate, and a frame for supporting the laminate and the top plate.  
         [0021]     There is provided a fifth aspect of the incubator according to any of the preceding claims, further comprising a nutrient medium supplying means for supplying nutrient medium into the container within the unit from outside thereof.  
         [0022]     There is provided a sixth aspect of the incubator according to the fifth aspect, wherein the nutrient medium supplying means has a structure for enabling the replenishment of nutrient medium within the container without removing the lid of the unit.  
         [0023]     There is provided a seventh aspect of the incubator according to any of the preceding claims, the container-accommodating portion further comprising a pair of container holders disposed across the central portion of the unit and adjustable the spacing between the holders as desired.  
         [0024]     There is provided a eighth aspect of the incubator according to any of the preceding aspects, wherein the unit is adapted to be placed on the upper surface of the stage of the microscope so as not to contact with the plate type heater with a spacing defined therebetween, and the unit and the heater are separable.  
         [0025]     There is provided a ninth aspect of the incubator according to the eighth aspect, further comprising fixtures for securing the unit on the upper surface to the stage of the microscope.  
         [0026]     There is provided a 10th aspect of the incubator according to any of the preceding aspects, further comprising a means for varying the position of the specimen container by displacing the container horizontally on the accommodating portion from outside of the unit.  
         [0027]     There is provided a  11 th aspect of the incubator according to any of the preceding aspects, wherein an entrance opening is provided through the side wall of the unit for putting the container into and out of the accommodating portion, and a side closure member for closing and opening the entrance is also provided.  
         [0028]     There is provided a 12th aspect of the incubator according to the  11 th aspect, wherein the heater is adapted to be fit into a tool fitting hole so as to flush an upper surface of the heater on, which the container will be placed, with the upper surface of a portion of the stage of the microscope.  
         [0029]     There is provided a 13th aspect of the incubator according to any of the preceding aspects, wherein the lid covering the upper end of the unit has one or more slots formed through which any operation will be carried out to the specimen, the position of each slot is offset from the region of the accommodating portion on which the specimen container is to be placed, the lid is adjusted to shift, while closing still the opening on the upper end of the unit, to displace the slots directly above the region of the accommodating portion on which the specimen container is to be placed.  
         [0030]     There is provided a 14th aspect of the incubator according to any of the preceding aspects, wherein the lid covering the upper end of the unit has an aperture formed in the region of the accommodating portion on which the specimen container is to be placed, the aperture is covered with a cover plate being rest on the lid, the cover plate can be displaced relative to the upper surface of the lid within the predetermined range while closing the aperture, the cover has a hole formed therein for inserting the objective lens.  
         [0031]     There is provided a 15th aspect of the incubator according to any of the preceding claims, wherein on the bottom surface of the water tank is provided a water tank heater.  
         [0032]     There is provided a 16th aspect of the incubator according to any of the third to 15th aspects, wherein the heater for heating the specimen container and the water tank unit has a container placing portion at which a heating portion is formed of a transparent conductive film.  
         [0033]     There is provided a 17th aspect of the incubator according to any of the preceding claims, wherein that the light ray transmitting portion of the lid closing the upper end of the unit has a heating portion formed of a transparent conductive film.  
         [0034]     There is provided a 18th aspect of the incubator according to any of the preceding aspects, further comprising a means for securing the specimen container to urge the container against the objective lens, when interposing any oil or water between the objective lens of the microscope and the specimen container.  
         [0035]     The first incubator assembly for observation by microscope, comprising the incubator according to any of the ninth to 17th aspects, and a jig assembly for securing the fixtures for the incubator in the desired position including a centering member and an outer jig member. The centering member is used to align the center of the water tank unit with the center of tool fitting hole. The outer jig member is fit around the peripheral portion of the unit to position the fixtures. After the center of the water tank unit is aligned with the center of tool fitting hole by the centering member, the fixture is in contact and fit around the outer jig member for positioning.  
         [0036]     The second incubator assembly for observation by microscope, comprising the incubator according to any of the first to 17th aspects, and a specimen container accommodated within the incubator. The specimen container includes a body opened at its upper surface and a lid for covering the upper surface. The lid is provided integrally with a pair of protrusions for connecting tubes at its upper surface. The protrusion includes an aperture for connecting the tube. The protrusion further includes a channel extending from the aperture to the lower surface of the lid.  
         [0037]     The third incubator assembly for observation by microscope, comprising the incubator according to the 11th or 12th aspect, and a tongs for putting the specimen container into and out of the incubator. The tongs includes a pair of arms formed of elastically deformable material connected at the rear ends or proximal ends thereof. These arms are crossed with each other at the crossing portion provided through the middle portion of these arms. The arms further include a pair of urging portions to have the arms approach with each other and close by the force generated by the elastic deformation of the material of the tongs. The portions between the urging portions and the crossing portions make a pair of parallel pinching portions, preventing the urging portions to be removed in more-closed direction from the given position.  
         [0038]     The fourth incubator assembly for observation by microscope, comprising at least two selected from the jig assembly for securing the fixtures of the first assembly, the specimen container of the second assembly, the means for securing the specimen container of the  18 th aspect, and the tool for clamping the specimen container of the third assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]     Further feature of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following specification with reference to the accompanying drawings, in which:  
         [0040]      FIG. 1  is a perspective view showing the incubator for observation by microscope in accordance with the first embodiment of the present invention;  
         [0041]      FIG. 2  is an plan view showing the incubator for observation by microscope in accordance with the first embodiment;  
         [0042]      FIG. 3  is a partially cross sectional view taken substantially along line A-A of  FIG. 1 ;  
         [0043]      FIG. 4  is an exploded perspective view showing the incubator in accordance with the first embodiment;  
         [0044]      FIG. 5  is a partially eliminated enlarged cross sectional view taken along line B-B of  FIG. 2 ;  
         [0045]      FIG. 6  is an enlarged cross sectional view taken along line C-C of  FIG. 2 ;  
         [0046]      FIG. 7  is a partially cross sectional view taken substantially along line B-B of  FIG. 3  wherein the off-the hook limiting lever is in its lock release position;  
         [0047]      FIG. 8  is an exploded perspective view showing the operation to be effected to secure the fixtures using a jig assembly for securing the fixtures;  
         [0048]      FIG. 9  is an exploded perspective view showing the operation to be effected to secure the fixtures using a jig assembly for securing the fixtures;  
         [0049]      FIG. 10  is a perspective view showing an example of the dish used in the incubator in accordance with the first embodiment of the present invention;  
         [0050]      FIG. 11  is an exploded perspective view showing the container body and the lid of the dish;  
         [0051]      FIG. 12  is an enlarged cross sectional view taken substantially along line D-D of  FIG. 10 ;  
         [0052]      FIG. 13  is a perspective view showing the incubator in accordance with the second embodiment of the present invention placed on the stage of the microscope;  
         [0053]      FIG. 14  is a perspective view showing the operation to be carried out for fixing the incubator in accordance with the second embodiment of the present invention on the stage of the microscope;  
         [0054]      FIG. 15  is a perspective view showing the operation to be carried out for fixing the incubator in accordance with the second embodiment of the present invention on the stage of the microscope;  
         [0055]      FIG. 16  is an exploded perspective view showing a water tank unit of the incubator in accordance with the second embodiment of the present invention;  
         [0056]      FIG. 17  is a plan view showing the incubator for observation by microscope in accordance with the second embodiment;  
         [0057]      FIG. 18  is a bottom plan view showing the water tank unit of the incubator for observation by microscope in accordance with the second embodiment;  
         [0058]      FIG. 19  is a cross sectional view taken substantially along line E-E of  FIG. 13 ;  
         [0059]      FIG. 20  is an enlarged view taken partially from  FIG. 19 ;  
         [0060]      FIG. 21  is a perspective view showing the structure and the method for using the dish tongs;  
         [0061]      FIG. 22  is a perspective view showing the structure and the method for using the dish tongs;  
         [0062]      FIG. 23  is a perspective view showing the structure and the method for using the dish tongs;  
         [0063]      FIG. 24  is an exploded perspective view showing the operation to be effected to put the dish by means of dish tongs into and out of the incubator in accordance with the second embodiment of the present invention;  
         [0064]      FIG. 25  is a cross sectional view showing the operation to be effected to put the dish by means of dish tongs into and out of the incubator in accordance with the second embodiment of the present invention;  
         [0065]      FIG. 26  is a perspective view showing the operation to be carried out to the specimen in the dish disposed within the incubator in accordance with the second embodiment of the present invention;  
         [0066]      FIG. 27  is a perspective view showing the incubator in accordance with the third embodiment of the present invention placed on the stage of the microscope;  
         [0067]      FIG. 28  is a cross sectional view taken substantially along line E-E of  FIG. 27 ; and  
         [0068]      FIG. 29  is a perspective view showing the dish and the weight to be placed on the dish when any oil or water is interposed between the bottom surface of the dish and the objective lens. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0069]     An incubator  201  for observation by microscope in accordance with a first embodiment of the invention will now be described with reference to  FIGS. 1-12 . The incubator  201  is used in inverted microscope.  
         [0070]     The incubator  201  includes a water tank unit  203  to which a dish  220  is to be detachably mounted, a lid  233  for covering the unit  203 , a heater plate  259  for heating the unit  203  and the dish  220 , and fixtures  281 ,  283  for securing the unit  203  on a stage  267  of a microscope.  
         [0071]     At first, the structure of the dish  220  used in the incubator  201  will be described with reference to  FIGS. 10-12  as follows.  
         [0072]     The dish  220  includes a circular, middle-depth dish body  221  of transparent plastic material, and a cover  223  therefor. The cover  223  includes at its upper surface a pair of half-pipe shaped protrusions  225  for connecting tubes. These protrusions  225  are disposed diametrically opposite with each other. Each protrusion  225  have a through hole  227  for connecting the tube formed therein. The through hole  227  has a L-shaped channel extending from the protrusion  225  as one open end to the lower surface of the cover  223  as the other open end (see  FIG. 12 ). The one ends of the holes  227  are directed in the opposite directions respectively.  
         [0073]     A tube  229  for delivering nutrient medium is inserted through the one hole  227  along the channel and protrude from the lower surface of the cover  223 . A tube  231  for withdrawing nutrient medium is inserted through the other hole  227  along the channel and protrude from the lower surface of the cover  223 .  
         [0074]     The dish  220  may be formed of transparent glass.  
         [0075]     An incubator assembly for observation by microscope includes the dish  220  and the incubator  201 .  
         [0076]     The water tank unit  203  includes a water tank  205 , a container holder for holding the dish  220 , a water-supplying pipe  213 , a gas-supplying pipe  214 , and tube holder  291 .  
         [0077]     The water tank  205  has a member comprising an annular bottom plate  205   a  and an outer peripheral wall  205   b  extending vertically from the outer edge of the bottom plate  205   a , and a cylindrical inner peripheral wall  205   d  extending upwardly from the edge of an opening  205   c  formed through the bottom plate  205   a . The outer area of the inner peripheral wall  205   d  makes an annular trough, which is referred hereinbelow as water reservoir  205   e , and the inner area of the inner peripheral wall  205   d  makes a container-accommodating portion  205   g.    
         [0078]     A splash depressor  205   i  for preventing the water contained in the water reservoir  205   e  from rushing over the wall  205   d  is provided on an upper edge of the inner peripheral wall  205   d.    
         [0079]     The upper edge of the outer peripheral wall  205   b  is provided with four recesses  205   f  (see  FIGS. 6 and 7 ) for threading tubes.  
         [0080]     A pair of holder seat  206  is secured on the inner peripheral surface of the inner wall  205   d  at the diametrically opposite position. Each seat  206  has a crescent configuration and a shallow and broad groove  206   a  is provided on its upper surface. A tapped hole  206   b  is also provided through the groove  206   a.    
         [0081]     A pair of container holders  207  of a crank shaped cross sectional configuration is adapted to be mounted on each seat respectively. Each holder  207  has at its upper leg an oblong slot  207   a  therethrough and at the tip  207   b  of its lower leg a rectangular notch. The upper leg of the holder  207  is adapted to be accommodated slidably within the groove  206   a  of the seat  206 , and secured fixedly thereto by a screw  208  threaded through the slot  207   a  into the hole  206   b . The spacing between the tips  207   b  of the lower legs can be adjusted by loosening the screw, displacing the holder as desired, and then fastening it again.  
         [0082]     A pair of tube holders  209  is provided on the outer peripheral surface of the wall  205   b , the one for the tube  229  for delivering nutrient medium, and the other for the tube  231  for withdrawing nutrient medium. The holders  209  are disposed to be diametrically opposite with each other. Each tube holder  209  includes a base block  210  secured on the outer peripheral surface, and a keep plate  212  adapted to be urged on the upper surface of the base block  210  by means of a presser screw  211 . The base block  210  has a holding recess  210   a  (see  FIG. 6 ) formed therein. The construction of the tube holder  209  for the tube  231  for withdrawing nutrient medium as illustrated in  FIG. 6  is same as that for the tube  229  for delivering nutrient medium.  
         [0083]     The holding recess  210   a  of each tube holder  209  is adapted to be in line with each recess  205   f  formed through the wall  205   b  of the water tank  205 .  
         [0084]     The tubes  229  and  231  for delivering and withdrawing nutrient medium to the dish  220  are threaded through the recesses  205   f  and  210   a , and secured thereto so as not to be withdrawn therefrom.  
         [0085]     The tube  229  is connected to the tank for reserving nutrient medium through a filter (not shown) for removing contaminant such as germs or bacteria.  
         [0086]     The means for supplying nutrient medium includes the tube  229  for delivering nutrient medium, the tube  231  for withdrawing nutrient medium, and the tank for reserving nutrient medium.  
         [0087]     The nutrient medium may also be supplied by a syringe. For example, the nutrient medium contained in the syringe may be delivered by pushing a plunger to displace the medium through the tube  229  into the dish  220 .  
         [0088]     A pair of pipe holders  291  for supporting a water pipe  217  and a gas pipe  218  is also mounted on the outer peripheral surface of the wall  205   b . These holders are juxtaposed in a predetermined distance from each other. Each pipe holder  291  includes a base block  293 . The base block  293  has a horizontally extending lateral channel  295 , which is formed through the wall  205   b  of the water tank  205  and leads to the recess  205   f . The base block  293  has also a tapped hole  297  extending from the upper surface to the channel  295 .  
         [0089]     The water-supplying pipe  213  inserted through one channel  295  and one recess  205   f  is adapted to be secured by pressing the pipe by the tip of the presser screw  296  attached to the tapped hole  297  (see  FIG. 7 ). Although the construction of the pipe holder  209  assigned for the water tube  217  is illustrated in  FIG. 7 , that assigned for the gas tube  218  can also be provided in the same construction.  
         [0090]     The gas pipe  214  is also inserted through the other channel  295  and the other recess  205   f , and secured by pressing the gas pipe by the tip of the presser screw  296  attached to the tapped hole  297  (see  FIG. 7 ).  
         [0091]     The water pipe  213  is curved downwardly at its tip portion protruding into the water tank  205  to dispose the tip opening  13 a thereof below the upper edge of the wall  205   d  and above the bottom of the water reservoir  205   e . The one end of the water supplying tube  217  is attached to the rear end of the water pipe  213  protruding from the channel  295  of the holder  209 , and the other end of the tube  217  is attached to the infusion reservoir  216 .  
         [0092]     The water supplying means includes the water pipe  213 , the infusion reservoir  216 , and the water-supplying tube  217 .  
         [0093]     The gas pipe  214  is curved downwardly at its tip portion protruding into the water tank  205  to dispose the tip thereof near the bottom surface of the water reservoir  205   e . One end of the gas-supplying tube  218  is attached to the rear end of the gas pipe  214  protruding from the channel  295  of the holder  209 . The other end of the tube  218  is attached to a bomb for containing the carbon dioxide gas through a valve for preventing the reverse flow of water within the water reservoir  205   e , a flow meter, and a control valve for adjusting the flow rate of the carbon dioxide gas.  
         [0094]     The gas supplying means includes the gas pipe  214 , the gas supplying tube  218 , the control valve, and the bomb for containing the carbon dioxide gas.  
         [0095]     The lid  233  includes a relatively thick annular lid plate  237  having a circular window  239  formed therein. A ring shaped protrusion  241  of the outer diameter smaller than that of the lid is formed on the lower surface of the lid plate  237 . The window  239  is closed by a transparent heater plate  243  of glass attached to the lower surface of the lid plate  237 .  
         [0096]     The heater plate  243  includes a pair of glass plates  244  and  246 , and a transparent conductive film formed on the lower surface of the upper glass  244  for converting electric energy into thermal energy. In order to control the electric current for delivering to the conductive film to adjust the thermal energy produced thereby and the temperature, a temperature sensor  257  is provided on the lower surface of the heater plate  243 .  
         [0097]     The heater plate  243  has a circular work hole  245  formed therein and offset relative to the periphery of the window  239 . The heater plate  243  has a pair of tube holes  250  formed therein. When effecting culture operation without the cover  223 , or exposing the dish  220 , the tubes  229  and  231  are inserted through the tube holes  250 , and the tip of these tubes are disposed within the dish  220  to exchange nutrient medium or culture media (B).  
         [0098]     The work hole  245  is closed by a lid  249  and the tube holes  250  are closed by plugs  251 .  
         [0099]     The diameter of the lid  249  is slightly larger than that of the work hole  245 . The work hole  245  is closed by disposing the lid  249  so as to surround the edge of the opening of the work hole  245  by an adhesive ring  253  of silicone rubber attached to the outer peripheral portion of the lower surface of the lid  249 . The lid  249  also has formed therein a smaller work hole  255 , which is closed by the plug  251 .  
         [0100]     The plug  251  is a disk shaped silicone rubber slightly larger than the tube holes  250  and the work hole  255 .  
         [0101]     A signal wire extending from the temperature sensor  257  is connected to the temperature controlling means (not shown).  
         [0102]     The heater plate  259  includes a ring shaped frame  261  of plastic. The outer diameter of the frame  261  is slightly smaller than the inner diameter of the water tank unit  203 . A ring shaped annular protrusion  263  extends downwardly from the lower surface of the frame  261 . The plate is further provided with an inner flange  265  extending from the inner peripheral surface of the frame near the upper surface thereof. The outer diameter of the protrusion  263  can be set to the diameter of the tool-fixing hole  269  of the stage  267  of the microscope.  
         [0103]     A top plate  271  of transparent glass is rest on the inner flange  265  of the frame  261 . An upper plate  275  is provided below the top plate  271  with interposing a thin spacing  272  therebetween. The top plate  271  is somewhat thicker than the spacing  272 . The top plate  271  also has a circular hole  273  at the central portion thereof.  
         [0104]     A laminate including the upper and lower plates  275  and  277  of anodized aluminum material, and a heater  279  of nichrome material interposed between plates is disposed below the inner flange  265  of the frame  261 . The upper plate  275  is adhered on the lower surface of the inner flange  265 , and thus the laminate including the upper and lower plates  275  and  277 , and the heater  279  are mounted on the inner flange  265  so as to depend therefrom. The upper and lower plates  275  and  277  are of annular configuration and have been alumite-treated.  
         [0105]     The upper and lower plates  275  and  277  have holes  275   a  and  277   a  of relatively larger diameter than that of the hole  273  of the top plate  271 .  
         [0106]     The light-transmitting channel is defined by the holes  275   a ,  277   a , the hole  273  of the top plate  271 , the window provided through the lid plate  237 , and the opening  205   c  defined through the bottom plate  205   a.    
         [0107]     Although not shown in the attached drawings, the frame  261  is also provided with a spacing through which cords extending from the temperature controller (not shown) to the heater  279  are laid.  
         [0108]     Each of Fixtures  281 ,  283  has a thick sheet body of rectangular cross section larger in its height than the width and of the same radius of curvature as that of the outer peripheral surface of the water tank  205 . The bottom surface of the fixture  281 ,  283  is provided with a both sides adhesive tape. Each of the fixtures  181 ,  283  has a pair of horizontally extending tap holes  284  through which a pair of presser screws  285  are to be threaded.  
         [0109]     The concrete structure of a jig assembly for securing the fixtures  281 ,  283  on the desired position on the stage  267  of microscope will now be described.  
         [0110]     The jig assembly includes a centering member  290  and an outer jig member  294 . The centering member  290  has an annular disk shaped body of the substantially same size as that of the dish  220 , and it have a circular hole  292  formed at the center thereof. The diameter of the hole  292  is the same as that of the hole  275   a  of the upper plate  275 . The outer jig member  294  has a ring shaped body to be fit snugly around the outer periphery of the water tank  205 . The members  294  also have along the outer periphery thereof, a pair of diametrically opposite recesses  298  for accommodating the fixtures  281 ,  283 . The width of the portion of the member  294  at which the recess  298  is formed is around 5 mm.  
         [0111]     The incubator assembly for observation by microscope includes the jig assembly for securing the fixtures and the incubator  201 .  
         [0112]     The method for using the incubator  201  will now be described.  
         [0113]     At first, the operation for securing the fixture  281  and  283  to the stage  267  of the microscope by using the jig assembly will be described with reference to  FIGS. 8 and 9 .  
         [0114]     The heater plate  259  is placed on the stage  267  of the microscope with inserting the ring shaped annular protrusion  263  of the frame  261  into the tool of the stage  267 . The outer jig member  294  is then placed on the stage  267  to the position of the frame  261 . Subsequently, the water tank  205  is placed over the heater plate  259  to fit the outer peripheral portion of the tank  205  into the outer jig member  294 .  
         [0115]     Subsequently, the centering member  290  is placed on the top plate  271  at the center of the container-accommodating portion  205   g ; the container holders  207  are displaced to contact the tips  207   b  with the outer peripheral surface of the centering member  290 . Then the screws  208  are tightened to secure the holder  207  to keep the centering member  290 . The water tank  205  is then adjusted to coincide the hole  292  of the centering member  290  with the hole  275   a  of the upper plate  275 .  
         [0116]     The outer jig member  294  is then indexed or rotated to bring the recess  298  of the member  294  to the position in which the fixtures  281  and  283  are to be secured.  
         [0117]     The presser screws  285  are threaded horizontally into the fixtures  281  and  283  so as not to protrude the tips beyond the surface of the fixtures  281  and  283  facing to the water tank  205 . Thus positioned fixtures  281  and  283  are fit to the recess  298  and secured on the stage  267  by means of the adhesive tape, and then the centering member  290  is removed.  
         [0118]     After the fixtures  281  and  283  are secured on the stage  267 , the water tank  205  is lifted from the stage  267  to remove the outer jig member  294 , and then the tank  205  is again brought down on the stage  267  as it were. Thus, the fixtures  281  and  283  are spaced by 5 mm from the outer peripheral surface of the tank  205 . Then the presser screws  208  are turned to extend the tips from the fixtures  281  and  283  to the outer peripheral surface of the tank  205  to position the water tank unit  203  securely on the stage  267 . If it is requested to change an observed portion, the position of the unit can be adjusted within the range allowed by the clearance between the fixtures  281 ,  283 , and the tank  205 , which is 5 mm to the fixtures  281 ,  283  respectively.  
         [0119]     The operation for securing the dish will now be described.  
         [0120]     After the screws  208  are loosened to free the holder  207 , the dish  220  is placed on the top plate  271  within the container-accommodating portion  205   g  of the water tank  205 . Then the holders  207  are moved toward the dish  220  to urge the tips  207   b  against the outer peripheral surface of the dish body  221 , and then the screws  208  extending through the oblong slot  207   a  into the hole  206   b  are fastened to hold the dish  220  by the holders  207 . The tubes  229  and  231  for delivering and withdrawing nutrient medium extend from the dish  220 . These tubes are then threaded through the recesses  205   f  and  210   a  and secured to the base block  210  by means of keep plate  212 .  
         [0121]     The specimen such as cells to be observed is preliminary contained in the dish  220  with some nutrient medium.  
         [0122]     The method for supplying water and carbon dioxide gas into the incubator  201  will now be described.  
         [0123]     The water contained in the infusion reservoir  216  hanged on any hanger above the water tank unit  203  is delivered by gravity through the water supplying tube  217  and the water pipe  213  to the water reservoir  205   e  within the unit  203 . The reservoir  205   e  is thus filled with water. Upon reaching the level of the water in the reservoir  205   e  to the level of the tip opening  213   a  of the pipe  213 , the supplying of the water is stopped spontaneously. The lowering of the level of the water through evaporation is compensated by the water contained in the infusion reservoir  216 . Thus the level of the water in the reservoir  205   e  is maintained in a predetermined level, and the amount (W) of water contained in the reservoir  205   e  is kept constant. The water may be delivered by means of syringe with reference to the amount of water contained in the reservoir  205   e  or periodically.  
         [0124]     In the incubator  201 , the water pipe  213  is seen through the heater plate  243  of transparent glass from outside of the incubator  201 . This is because the window  239  is formed to be circular. In this connection, the level of water contained in the reservoir  205   e  can be easily ascertained at a glance.  
         [0125]     The operation of the incubator  201  in accordance with the first embodiment will now be described.  
         [0126]     When heating the water contained in the reservoir  205   e  to generate water vapor, the heater plates  243  and  259  are energized under the control of the controller (not shown) to heat the dish  220  and the water tank  205  to evaporate the water in the reservoir  205   e . The incubation space  235  is thus filled with water vapor and the dish  220  is exposed thereto. The relative humidity of the incubation space  235  can be kept in the range between 90 and 95% and the temperature in dependence on the amount of heat energy provided through the heater plates  243  and  259 . The humidity within the dish  220  can be maintained in the uniform humidity, since the dish  220  is positioned in the center of the incubation space  235  surrounded by the reservoir  205   e.    
         [0127]     The concentration of carbon dioxide gas within the incubation space  235  can be kept in 5%. This can be done by delivering the carbon dioxide gas of 5% through the control valve and the gas tube  218  into the space  235 . Although the concentration of carbon dioxide gas within the space  235  is leaked out from the space through the clearance between the water tank  205  of the incubator  201  and the lid  233 , the gas is continuously delivered. Thus the space  235  is maintained at the 5% gas concentration.  
         [0128]     The concentration of carbon dioxide gas within the space  235  can also be kept constant by any other methods. When it is necessary to keep the gas concentration within the space  235  substantially constant, carbon dioxide gas of much higher concentration can be delivered intermittently into the space  235  based on information from a sensor for detecting the gas concentration within the incubation space  235 .  
         [0129]     The gas to be delivered into the space  235  is not limited to carbon dioxide gas, and it may be nitrogen gas or oxygen gas.  
         [0130]     As can be seen from the above, the incubation of the specimen (e.g. germs or cells) can be effected under the predetermined temperature, humidity and concentration of carbon dioxide gas, and change of nutrient medium is done without removing the lid  233  or the cover  223  of the dish  220 . In other words, the amount of nutrient medium in the dish  220  is kept constant by withdrawing the deprived medium (B) through the tube  231  and delivering flesh medium through the tube  229  of the amount substantially identical with the withdrawn medium. Thus, the incubator  201  and the dish  220  allow the circulation incubation with changing nutrient medium.  
         [0131]     The tubes  229  and  231  can be inserted and withdrawn easily through the aperture  227  so that the amount of nutrient medium (B) can be controlled by adjusting the height (the distance from the bottom surface of the dish  220 ) of the tip opening  23   1 . In other words, the amount of the medium (B) can be increased by rising the level of the medium (B) and by increasing the height of the tip opening  231  of the tube  231 . Whereas the amount of the medium (B) can be decreased by lowering the level of the medium (B) by decreasing the height of the tip opening  23   1  of the tube  231 .  
         [0132]     When observing the specimen within the dish  220 , the ray of light irradiated from the condenser (C) pass through the hole  273  of the top plate  271 , the hole  275   a  of the upper plate  275 , and the hole  277   a  of the lower plate  277 , and is incident into the objective lens (T). Thus, variation of the specimen with time within the dish  220  can be observed and recorded while incubating the specimen.  
         [0133]     The heater plate  259  is spaced from the water tank unit  203  so that the variation of the weight of the unit  203  due to the variation of the amount of the medium contained in the reservoir  205   e  does not bring any effects on the heater plate  259 . Thus, the distance between the dish  220  and the objective lens (T) is maintained constant to prevent the observed image from unclear.  
         [0134]     The clearness of the observed image can also be enhanced by spacing the top plate  271  on which the dish  220  is placed above the upper plate  275  of the heater plate  259 . The influence to be applied on the dish  220  by thermal expansion or deformation of the top plate  275  due to the temperature variation of the heater plate  259  is smaller than the case in which the dish  220  is placed directly on the upper plate  275 . This is because the coefficient of expansion of the glass material forming the top plate  271  is lower than that of the aluminum material forming the heater plate  259 . Thus, the unclearness due to the variation of the distance between the specimen and the objective lens (T) can be avoided more effectively.  
         [0135]     The laminate comprising the upper plate  275 , the lower plate  277 , and the heater  279  deforms downwardly upon heated since the laminate is attached to the inner flange  265  to depend therefrom. The effect on the dish  220  through the deformation of the laminate including the upper plate  275  can be reduced to the minimum, and the unclearness of the image to be observed can be avoided.  
         [0136]     The deformation of the upper plate  275  does not influence the dish  220 . This is because there is the spacing  272  between the top plate  271  and the upper plate  275 . Thus, the effect for avoiding the unclearness due to the variation of the distance between the specimen and the objective lens (T) can be enhanced further.  
         [0137]     The observation through microscope with interposing any oil or water between the bottom surface of the dish  220  and the objective lens (T) may effected, because the incubator  201  for observation by microscope  201  includes the hole  273 , the hole  275   a , and the hole  277   a.    
         [0138]     In addition, the incubator  201 , upon removing the water tank unit  203 , can be used to observe the specimen on a slide glass or the like with heating it.  
         [0139]     An incubator  311  in accordance with a second embodiment of the present invention will now be described with reference to  FIGS. 13-26 . The incubator  311  is that to be used in erecting microscope.  
         [0140]     The same component or components of the incubator  311  as that of the incubator  201  of the first embodiment are designated by the same reference numerals, and the descriptions thereof will be omitted.  
         [0141]     The incubator  311  includes a water tank unit  347  to which a dish  313  is adapted to be placed removably therefrom, a lid  431  for covering the upper surface of the unit  347 , and a heater plate  317  for heating the unit  347  and the dish  313 . The incubator  311  is adapted to be mounted on the driving stage  319  including a pair of superposed stage plates  321  and  323 .  
         [0142]     The upper plate  321  is adapted to be displaced horizontally in the left to right direction (referred hereinbelow to as A-B direction), and the lower plate  323  is adapted to be displaced horizontally in the front to rear direction (referred hereinbelow to as C-D direction). Thus, the incubator  311  can be displaced in both of the A-B direction and the C-D direction. The upper plate  321  is also provided with a circular tool-fitting hole  269 .  
         [0143]     The construction of the heater plate  317  will be described.  
         [0144]     The frame designated by the reference numeral  325  is of aluminum alloy, and the outer diameter of which is slightly smaller than the inner diameter of the water tank unit  347 . The frame includes an inner flange  327  extending inwardly from the inner surface thereof. The inner flange  327  supports on its upper surface the outer periphery of the lower surface of a top plate  328  of glass material. The place  330  for supporting the container of the specimen to which the dish  313  is to be placed is defined on the central portion of the upper surface of the top plate  328 .  
         [0145]     A transparent heater plate  329  of glass laminate structure is secured on the lower surface of the inner flange  327 . The heater plate  329  includes a pair of transparent glass plates (i. e. upper glass plate  333  and lower glass plate  331 ) and a transparent conductive film  335  of an ITO film formed on the upper surface of the lower glass plate  331 . The transparent conductive film  335  is adapted to be energized through a pair of spaced terminals (or electrodes) provided thereon.  
         [0146]     There is spacing between the upper surface of the transparent heater plate  329  and the lower surface of the top plate  328 .  
         [0147]     The frame is provided its outer peripheral surface with an outer flange  337  and a stepped portion  339 , i. e. the frame has two kinds of shoulders different in their diameter, so that it is possible to fit the heater plate  317  into two kinds of tool fitting holes different in their diameter.  
         [0148]     As can be seen from  FIG. 14 , a portion  345  of the upper surface of the frame  325  is removed to the height of the upper surface of the top plate  328  to which the container of the specimen to be placed.  
         [0149]     The structure of the water tank unit  347  will now be described.  
         [0150]     The water tank unit  347  includes a unit body  348 , a water tank  361 , a container holder  351  for holding the dish  313 , a water supplying tube  213 , a gas supplying tube  214 , and tube holder  353 .  
         [0151]     The unit body  348  is of plastic material and has an opening  355  extending vertically through the central portion thereof. An entrance opening  359  is provided through the peripheral wall of the unit body  348 . The entrance opening  359  extends from the upper surface of the body to nearly the bottom surface thereof. Thus, a thin-sheet shaped bridging portion is left on the entrance opening  359 .  
         [0152]     The water tank  361  is a “C-shaped” shallow container because of the presence of the discontinuity  365 . The water tank  361  includes a bottom plate  362 , an inner peripheral wall  366 , an outer peripheral wall  364 , and closure plates  368  extending between the inner and outer walls. A water tank reservoir  390  is defined between the bottom plate  362   a , the inner peripheral wall  366 , the outer peripheral wall  364 , and closure plates  368 .  
         [0153]     The water tank  361  is contained within the opening  355 . The outer periphery of the bottom of the tank  361  is supported on the shoulder formed on the inner peripheral surface of the unit body  348  with contacting the outer peripheral wall  364  with the inner peripheral surface of the unit body  348 . The area defined within the inner peripheral wall  366  is a container-accommodating portion  392 .  
         [0154]     As shown in  FIG. 18 , a water tank heater  358  of an insulated nichrome wire is provided under the tank  361 . The heater  358  is covered with a heater cover  360  of plastic material.  
         [0155]     A means for displacing the specimen container will now be described.  
         [0156]     The means comprising a pair of symmetrical left and right displacing mechanisms  350  and  352 , so that the structure of the left mechanism will only be described and that for the right one will be omitted.  
         [0157]     The upper and left portion of the peripheral wall  357  is removed to form a shoulder  340  and then the upper surface of thus formed shoulder is formed with a guiding recess  342  extending in the C-D direction (see  FIG. 20 ). The portion of the peripheral wall  357  extending upwardly from the shoulder is provided with a long, through hole  367  extending laterally. The portion of the peripheral wall  357  extending downwardly from the shoulder is provided with an accommodating recess  369  extending in the A-B direction.  
         [0158]     A slider  371  includes a slider body  373  and mounting potion  375  (see  FIG. 19 ). The mounting potion  375  includes an upwardly extending portion  377  and a downwardly extending portion  379 . The slider  371  has therein a through hole  381  for passing the shaft  387 , and a tapped hole  383  extending from the upper surface of the slider body  383  to the through hole  381  to which the presser screw  385  is to be screwed.  
         [0159]     The shaft  387  is connected to the vertical portion  391  of the “L-shaped” control member  389 . The horizontally extending portion  393  of the control member  389  is inserted into the accommodating recess  369 . The container holder  351  is connected at the tip of the shaft  387 . The container holder  351  has a crank shaped cross sectional configuration. The holder  351  has at the tip  395  of its lower leg a rectangular recess.  
         [0160]     There is a presser member  397  having on the lower surface, a guiding recess  399  extending in the C-D direction. The presser member  397  has a tapped hole  401  leading to the recess  399  to which a presser screw  402  is to be attached.  
         [0161]     The downwardly extending portion  379  of the slider  371  is adapted to be fit within the guiding recess  342  formed on the shoulder  340 . The presser member  397  is secured on the upper surface of the peripheral wall  357  by means of attaching screws  403  with fitting the guiding recess  399  with the upwardly extending portion  377 . The slider  371  can be displaced in the C-D direction through the cooperation of the upwardly and downwardly extending portions  377 ,  379  and the recesses  342 ,  399 . The holders  351  are positioned on a container-accommodating portion  392  surrounded by the inner peripheral wall  366 .  
         [0162]     The means for displacing the specimen container is constructed as described above.  
         [0163]     The water tank unit  347  includes six tube holders  353  disposed three by three on each of left and right sides thereof. Each tube holder  353  includes a base block  405  secured on the outer peripheral wall and a presser screw  407 . The base block  405  has a through hole  409  extending in the A-B direction, and a tapped hole  411  extending from the upper surface thereof to the hole  409 . A presser screw  407  is to be attached to the tapped hole  411 . The unit body  348  has also therein six holes  413  for threading tubing. The two of the six holes are further provided with pipes  213  and  214  for delivering water and gas. These pipes are bent at their tip portion towards the water tank reservoir  399 . Those to be attached to the holes  409  of the base block  405  are a water tube  217 , a gas tube  218 , a nutrient medium delivering tube  229 , a nutrient medium withdrawing tube,  231  and a temperature sensor  415 . The water tube  217  is connected to the pipe  213 , and the gas tube  218  is connected to the pipe  214 . The pipes  217  and  218  and the temperature sensor  415  extends from the holes  214  provided through the unit body  348  to the container-accommodating portion  392 . The remaining one tube holder  353  is a reserve part.  
         [0164]     The front face of the unit body  348  is provided with a pair of magnet sheets  416  and  417 .  
         [0165]     A side closure member  419  includes an insert portion  421  and a handle portion  423  larger in its width than that of the insert portion  421 . Thus formed shoulder of the handle portion  423  is provided with a metal thin sheet  427  and  429  of iron. The handle portion  423  is provided with a pair of rectangular recesses  425 .  
         [0166]     The structure of a lid  431  will now be described.  
         [0167]     A lid plate  433  is of substantially annular shape, and both sides thereof is cut off in parallel. In other words, the sides of the plate  433  in the A-B direction are planer, and the sides in the C-D direction are circular (see  FIG. 15 ). The size of the plate  433  in the A-B direction is slightly larger than the distance between the presser members  397 . A circular window  435  is provided through the lid plate  433 . The lower surface of the inner portion of the plate  433  is removed to form an annular shoulder including at the lower side of the inner peripheral portion thereof an annular protrusion  437 . A heater plate  439  of transparent glass is attached to the lower surface of the protrusion  437 . The upper surface of the heater plate  439  forms a portion of the lid  431 .  
         [0168]     A transparent heater plate  439  of glass laminate structure includes a pair of transparent glass plates  441  and  443  and a transparent conductive film  445  of an ITO film formed on the upper surface of the lower glass plate  441 . The transparent conductive film  445  can convert electric energy to generate heat energy. The electric energy to be delivered to the film  445  of the heater  439  is adapted to be controlled based on information obtained from temperature sensor  447  provided on the heater  439 . Thus, the temperature may be controlled within the predetermined range.  
         [0169]     A circular aperture  449  is formed through the central portion of the heater plate  439 . The heater plate  439  has formed therein a pair of oblong slots  451  larger in its dimension in the A-B direction through which any operation will be carried out to the specimen.  
         [0170]     A cover plate  453  is made of thin transparent glass adapted to be disposed on the heater plate  439  for covering the aperture  449 . The cover plate  453  has a hole  455  for accepting the lens of the microscope. The pair of slots  451  is covered with a closure member  457 .  
         [0171]     The lid  431  is provided with cords  459  for supplying electric energy to the film  445  and for transmitting the signal from the temperature sensor  447  to the controller (not shown).  
         [0172]     The structure and the operation of a dish tongs  461  will now be described with reference to  FIGS. 21-23 .  
         [0173]     The tongs  461  of elastically deformable stainless steel has a pair of arms  463  connected at the rear ends or proximal ends thereof. These arms are crossed with each other at the crossing portion  465  provided through the middle portion of these arms. The arms further include a pair of urging portions  467  to be urged against each other by the force generated by the elastic deformation of the material of the tongs. The portions of the arms extending distally from the urging portions are bent away from each other and then bent back to form a pair of parallel pinching portions  469 . A pair of slip-proof caps  471  of synthetic rubber is fit on the pinching portions  469 . The minimum spacing between the pinching portions  469  can be kept constant by the abutment of the portions  467 .  
         [0174]     The tongs  461  and the incubator  311  for observation by microscope form an incubator assembly for observation by microscope.  
         [0175]     The method for using the incubator  311  of the second embodiment and the mode of operation of the incubator will now be described.  
         [0176]     At first, the manipulation effected to fit the incubator  311  on the driving stage  319  will be described.  
         [0177]     The heater plate  317  is placed on the tool fitting hole  269  formed through the upper plate  321  of the driving stage  319  as shown in  FIG. 14 . In this condition, the upper surface of the top plate  328  of the heater plate  317 , a portion  345  of the upper surface of the frame  325  removed to the height of the upper surface of the top plate  328 , and the upper surface of the upper plate  321 , are all placed in the same height, i. e. flush with each other. The dish  313  to be placed on the container-accommodating portion  392  of the water tank unit  347  is placed on the place  330  for supporting the container of the specimen.  
         [0178]     The water tank unit  347  is then mounted on the upper plate  321  to align the container-accommodating portion  392  with the place  330  for supporting the container of the specimen, and the lid  431  is then placed on the unit  347  to cover the upper opening of the unit  347 . The aperture  449  of the heater plate  439  is covered with the cover plate  453 , the pair of oblong slots  451  are closed by the closure member  457 , and the entrance  359  is closed by the side closure member  419 . The entrance  359  can surely be closed by the side closure member  419  through attracting the iron plates  427  and  429  onto the magnet sheets  416  and  417  provided on the unit body  348 .  
         [0179]     The incubator  311  is mounted on the driving stage  319  as described above. The space defined by the unit  347  and the lid  431  makes an incubation space  320 .  
         [0180]     The controller is then energized.  
         [0181]     The water tank reservoir  390  is adapted to be filled with water supplied from the water tank through the water tube  217  and the water pipe  213 . The incubation space  320  is filled with carbon dioxide gas from the bomb for containing carbon dioxide gas through the gas tube  218  and the gas pipe  214 .  
         [0182]     The transparent conductive film  335  of the transparent heater plate  329  of the heater plate  317  is energized through a pair of spaced terminals provided thereon to generate heat energy. The water tank heater  358  is energized to generate heat energy to heat the water tank  361  directly. The transparent conductive film  335  of the heater plate  439  of the lid  431  is energized through a pair of spaced terminals provided thereon to generate heat energy. The heater plate  329  and the water tank heater  358  are energized based on information detected by the temperature sensor  415 , and the heater plate  439  is energized based on information detected by the temperature sensor  447 .  
         [0183]     The water contained in the water tank reservoir  390  is vaporized by heat energy provided by the heaters  329 ,  358 , and  439 . More particularly, sufficient amount of vapor can be generated quickly by heating the water in the water tank reservoir  390  directly by means of the water tank heater  358 . The specimen within the dish  313  can be heated uniformly by heating whole of the bottom of the dish  313  through the transparent heater plate  329  of the heater plate  317 . The heater plate  439  of the lid  431  can be prevented from fogging.  
         [0184]     After the incubation condition in the incubation space  320  such as the temperature, the humidity, and the concentration of carbon dioxide gas had reached the predetermined value, the side closure member  419  is removed to open the entrance. Then the dish  313  is held by the tongs  461  to bring it through the entrance  359  into the container-accommodating portion  392 , and placed in the place  330  for supporting the container of the specimen (see  FIG. 25 ). The objectives such as cells are contained in the dish  313 .  
         [0185]     Depending on the kind of the specimen to be incubated, the dish  313  may be placed within the container-accommodating portion  392  without the lid or before fitting the lid.  
         [0186]     If squeezing the potion of the tongs  461  proximal to the crossing portion  465  of the arms  463 , the pinching portions  469  are displaced away from each other. Then the dish  313  is placed between the portions  469  and removing the squeezing force to hold the dish between the portions  469  by the force generated by elastic deformation of the material of the tongs. The dish  313  is carried by the tongs through the entrance  359  into the place  330 .  
         [0187]     Then the entrance  359  is closed by fitting the side closure member  419  into the unit body  348 . The fitting aperture of the side closure member  419  can be made by holding the handle portion  423  by fingers of the operator. The pair of rectangular recesses  425  of the handle will prevent the fingers from slipped out therefrom.  
         [0188]     The dish  313  can be removed from the container-accommodating portion  392  by means of the tongs  461  through the entrance  359 . As can be seen from the above, putting in and out of the dish  313  from the portion  392  can be made without affecting the balance among the incubation conditions in the space  320  such as temperature, the humidity, and the concentration of carbon dioxide gas, i. e. without affecting the incubation of the specimen.  
         [0189]     The upper surface of the top plate  328  of the heater plate  317 , a portion  345  of the upper surface of the frame  325  removed to the height of the upper surface of the top plate  328 , and the upper surface of the upper plate  321  are all placed in the same height as described above. Thus there are no steps. In this connection, putting in and out of the dish  313  from the portion  392  can be made smoothly without any obstruction.  
         [0190]     Subsequently, the presser screws  385  of the pair of left and right displacing mechanisms  350  and  352  of the means for displacing the specimen container are loosened to enable the shaft  387  to be displaced. Then the shaft  387  is displaced in the A-B direction by displacing the vertical portion  391  of the control member  389  to push the dish  313  through the holder  351  to shift the dish in the A-B direction to the desired position. Then the screws are tightened to hold the shaft  387  by the tip thereof to secure the position of the holder  351 . In the conditions, the dish  313  is interposed between the rectangular recesses provided at the tips  395  of the holders  351 .  
         [0191]     The lid  431  can be shifted along the presser members  397  in the C direction to align the oblong slots  451  with the dish  313 . The closure member  457  is removed to guide the tubes  229  and  23   1  for nutrient medium into the dish  313 .  
         [0192]     The specimen such as cells contained in the dish  313  can be observed by the objective lens (T) inserted into the hole  455  provided through the cover  453 .  
         [0193]     When it is intended to change the area of the specimen in the dish  313  to which the objective lens (T) is to be directed, it is only necessary to shift the driving stage  319  in the A-B direction and/or in the C-D direction as desired. It is not necessary to withdraw the objective lens (T) from the hole  455  provided through the cover  453 . Upon shifted the stage  319 , the incubator  311  is also shifted together with the stage  319  except for the cover  453 . In other words, upon shifted the stage  319 , the heater plate  439  shifts relative to the cover  453  since the objective lens (T) abut against the inner peripheral edge of the hole  455  of the cover  453 . Thus, the area to be observed can be changed by shifting the driving stage  319  within the range determined by the aperture  449  without removing the cover  453  from the aperture  449 . Thus, the balance between the incubation conditions in the space  320  such as temperature, the humidity, and the concentration of carbon dioxide gas can be kept as it was since the aperture  449  is kept close by the cover  453 .  
         [0194]     When drugs or chemicals are intended to be added to the specimen in the dish  313 , it is necessary to retract the objective lens (T) to withdraw it from the hole  455  as shown in  FIG. 26 , and the cover  453  is replaced by the closure cover  473  without any holes to close the aperture  449 . The lid  431  is shifted along the presser members  397  in the C direction to align the oblong slots  451  with the dish  313 , and drugs or chemicals are added into the dish  313  by the syringe (S) inserted through the slots  451 . Thus, any operation can be made to the specimen without spoiling the condition within the incubation space  320 .  
         [0195]     An incubator  511  for observation by microscope in accordance with the third embodiment of the present invention will now be described with reference to  FIGS. 27-29 . The incubator  511  is that to be used in the inverted microscope.  
         [0196]     The same component or components of the incubator  511  as that of the incubator  311  of the second embodiment are designated by the same reference numerals, and the descriptions thereon will be omitted.  
         [0197]     A transparent heater plate  513  of glass of the lid  510  of the incubator  511  does not have a central aperture, and a transparent heater  517  of glass of the heater plate  515  has therein a hole  519  for accepting the lens of the microscope.  
         [0198]     A means for securing the specimen i.e. a weight  521  of stainless steel is a ring, which is slightly larger in its diameter than that of the dish  313 .  
         [0199]     The weight  521  is served to depress the rising of the dish while the observation is effected by interposing any oil or water between the bottom surface of the dish  313  and the objective lens (T).  
         [0200]     An incubator assembly for observation by microscope comprises the weight  521  and the incubator  511 .  
         [0201]     The method for using the incubator  511  of the third embodiment will now be described.  
         [0202]     The weight  521  is placed on the dish  313  placed within the confine of the container-accommodating portion  392 . Some oil is applied to the tip of the objective lens (T) and then the objective lens (T) is moved toward the dish  313  to make the oil layer between them. The observation of the specimen in the dish  313  such as cells is then effected.  
         [0203]     The operation for shifting the dish  313  in order to change the area of the specimen in the dish  313  to be observed will now be described.  
         [0204]     When it is intended to displace the dish  313  in the A-B direction, the presser screws  385  of the pair of left and right displacing mechanisms  350  and  352  of the means for displacing the specimen container are loosened to enable the shaft  387  to be displaced. Then the container holder  351  is displaced together with the shaft  387  in the A-B direction through the vertical portion  391  of the control member  389  to push the dish  313  through the holder  351  to shift the dish in the A direction or the B direction to a desired position. Then the screws  385  are fastened to hold the shafts  387  by the tips thereof to secure the position of the holder  351 . In the conditions, the dish  313  is interposed between the rectangular shaped recesses provided at the tips  395  of the holders  351 .  
         [0205]     When it is intended to displace the dish  313  in the C-D direction, the presser screws  385  are fastened to hold the shafts  387  by the tips thereof to secure the positions of the pair of holders  351  to hold the dish  313 . Then the presser screws  402  are loosened to release the tips of the screws  402  from the upwardly extending portions  377  to enable the slider  371  to shift in the C-D direction. Subsequently, the slider  371 , the shaft  387 , and the container holder  351  are displaced in the C direction or the D direction to a desired position by means of the control members  389  of the pair of left and right displacing mechanisms  350  and  352 .  
         [0206]     As can be seen from the above, even if observation is effected by the inverted microscope in which the objective lens (T) are directed to the dish  313  from the lower side of thereof, the position of the dish  313  can be changed from the outside of the unit  347 , and the position of the area of the dish  313  to be observed can also be changed without removing the lid  510 .  
         [0207]     The fogging of the transparent heater plate  513  of the lid  510  caused by the generated steam may be prevented by the heat generated thereby so that the observation can be effected under the clear plate.  
         [0208]     The transparent heater  329  of glass is secured on the lower surface of the inner flange  327 . That is, it is depend therefrom. Accordingly, the heater plate  317  expands or deforms downwardly upon heated by the heater  329 . Further, there is a space between the plate  329  and the top plate  328 . As a result, the expansion or deformation of the heater  329  does not affect the top plate  328 .  
         [0209]     Consequently, the dish  313  containing the specimen is prevented from moving along an optic axis of the objective lens (T). Thus the distance between the specimen to be observed and the objective lens (T) can be maintained constant to prevent the observed image from unclear.  
         [0210]     While particular embodiments of the present invention have been illustrated and described, it should be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.  
         [0211]     In the first embodiment, although the dish  220  with the cover  223  is used, the dish  220  may fit into the container-accommodating portion  205   g  without the cover  223 . In the conditions, drugs or chemicals are introduced, after removing the cover  223 , by inserting some tool through the work hole  245  of the heater plate  243 , so that the operation can be effected without affecting the conditions such as the temperature within the space  235 .  
         [0212]     In the first embodiment, described is the circulation incubation by withdrawing the predetermined amount of nutrient medium through the tube  231  and at the same time delivering the same amount of nutrient medium through the tube  229 . However, the present invention will not limited to such a structure, and a stationary incubation without requiring the exchange of nutrient medium may be made. In such a case, tubes  229  and  231  are omitted.  
         [0213]     Further, the structure with no water supplying means such as water supplying pipe  213  and the infusion reservoir  216  may be employed. In such structure, water is supplied at first into the reservoir  205   e  and does not supplied additionally. This is because the incubation can be carried out for about 48 hours without supplying water. The window  239  formed through the lid plate  237  may be a rectangular configuration rather than a circular configuration.  
         [0214]     In the first embodiment, the heater plate  259  includes at its center a through hole, and has the upper plate  275  of aluminum material. However, the structure of the heater cannot be limited to such structure. For example, the heater including a transparent conductive film deposited on the surface of the glass plate may be used.  
         [0215]     There may be provided without the work hole  245  through the heater plate  243 .  
         [0216]     Although the dish  220  is placed on the top plate  271  in the first embodiment, the dish may be placed directly on the upper plate  275  with removing the top plate  271 .  
         [0217]     In order to avoid the observed image to be blurred through deformation of the upper and/or lower plates  275  and/or  277  in micron order by depriving the heater plate  259  of its heat energy through the contact with the objective lens (T), a lens heater may be wound around the cylindrical body of the objective lens (T).  
         [0218]     In the second and third embodiments, the means for displacing the specimen container includes a pair of left and right displacing mechanisms  350  and  352 , so that it is necessary to manipulate both mechanisms for shifting the dish  313 . However, the dish maybe held in cantilever fashion by only one mechanism. In such case, the manipulation of the dish is made by the one mechanism.  
         [0219]     Although the weight  521  is used to secure the specimen container in the third embodiment, the present invention is not limited thereto. Any means other than the weight such as spring can be used for securing the container and preventing it from rising.  
         [0220]     The top plates  271  and  328  may be made of brass material. In such a case, it is necessary to provide a hole on the central portion of the top plate for transmitting the light ray therethrough. Further, the frame  261  of the heater plate  259  and the frame  525  and the heater plate  317  can also be made of brass material.  
         [0221]     Although the heater plates  317  and  515  including a transparent heater element of glass are illustrated in the second and third embodiments, other heating means such as the heater plate  259  including a nichrome wire as a heating element may also be used.  
         [0222]     In the above-mentioned embodiments, the incubator assembly comprises the combinations of the dish  220  and the incubator  201 , the jig for securing the fixtures and the incubator  20 l, the dish tongs  461  and the incubator  311 , or the weight  521  and the incubator  511 . However, the assembly are not limited to the above recited combinations, and the incubator  201 ,  311  or  511  can be combined with either of the dish  220 , the jig, the dish tongs  461 , or the weight  521  as desired. Further, the assembly may comprise either one of the incubator  201 ,  311  or  511  and one or two or more of the dish  220 , the jig, the dish tongs  461 , or the weight  521 . When it is desired to combine the jig with the incubator  311  or  511 , the configuration of the outer jig member  294  may be varied to that of the water tank unit  347 .  
       INDUSTRIAL APPLICABILITY  
       [0223]     The incubator of the present invention will provide following advantages.  
         [0224]     Incubation and observation of the specimen can be carried out on the stage of microscope.  
         [0225]     Any manipulations or operations can be easily effected on the specimen without breaking the predetermined incubation conditions.  
         [0226]     The portion of the specimen in the container to be observed by the microscope can be changed without breaking the predetermined incubation conditions.  
         [0227]     Sufficient amount of vapor can be generated quickly within the incubation space.