Abstract:
A microscope stage capable of always heating the entire culture vessel even when the culture vessel is moved in two-dimensional directions, and allowing an object lens and a condenser even in a high-power microscope to approach an object of observation such as a cell until they come into focus. A heating unit ( 58 ) faces a well plate ( 37 ) on a drive base ( 49 ) even when the drive base ( 49 ) is driven to any position in two-dimensional directions. Therefore, all the cells A in the small compartments ( 45 ) of the well plate ( 37 ) are always heated. Since the microscope stage ( 25 ) is constituted such that a lower-side base ( 71 ) houses an upper-side base ( 73 ) and a fixed base ( 47 ) in recessed portions, its thickness is considerably small. Accordingly, an object lens ( 5 ) and a condenser ( 3 ) can approach close to the cells A. Therefore, it is possible for high-power object lens ( 5 ) and condenser ( 3 ) to focus on the cells A.

Description:
BACKGROUND 
     The present invention relates generally to a microscope stage capable of heating an entire culture vessel containing specimen such as cells or microorganism to be observed, and a microscope observing unit including the microscope stage and a culture device to be disposed on the stage. 
     It has been well known in the art to use shallow cylindrical dishes of a diameter of 35 mm as culture vessels for cells or microorganisms. Recently, there have been used culture vessels so called well plates having a number of cells or compartment, each well cells Accommodating a culture solution and cells or microorganisms. The typical dimension of the well plates is of a width of 85 mm and a length of 115 mm. Namely, the well plates are substantially larger than the dishes. The well plates have a variety of depths. As can be seen from above, there has been used culture vessels of various sizes in dependence upon their applications. 
     When it is intended to culture cells or microorganisms, it is required to keep a given temperature within the dishes or well plates, for example, at 37° C. It is further required to control atmosphere within the dishes or well plates in terms of CO 2  concentration, the humidity and the like. 
     Generally, light microscopes are used for observation of cells and the like. When observing growing cells or microorganisms, it is required to heat a culture vessel accommodating the cells therein disposed on the microscope stage. In order to accomplish the heating of the vessel, commercially available is stage heaters adapted to be fit into the opening formed in the central portion of the microscope stage. Each stage heater includes a glass plate on which an electrically conductive transparent film applied. Upon energized, the film generates heat energy to heat the culture vessel disposed thereon. 
     However, especially for a well plate of larger size, the entire well plate is not heated by the commercial stage heaters, i.e. at least a portion of the well plate is not heated. This is because the stage heater as mentioned above is positioned only on the central portion of the microscope stage. Thus, a portion of the cells or microorganisms can not be disposed oppositely with the stage heater. 
     Further, for well plates, observation is done for each well cells Accommodating cell or microorganisms and culture solution. In this connection, it is required to displace the well plate repeatedly in order to align one well cell to be observed with the optical axis of the microscope objective lens by the cell number. It is cumbersome to displace the well plate manually. Further, it is difficult to displace the well plate precisely by hands. In this connection, it is requested to use a microscope stage of such a type that the base member, on which a culture vessel is disposed, can be shifted in two dimensional directions. 
     However, the two dimensionally movable microscope stage of this kind is relatively thick, since it is of a three-stage structure including a fixed base to be secured on the microscope, a lower base adapted to be movable in side to side direction (referred hereinafter to as x-direction), and an upper base adapted to be movable in back and force direction (referred hereinafter to as y-direction). If the stage heater of the type above mentioned is simply incorporated into the movable type microscope stage, the overall thickness of the microscope stage will further thicken. Thus, the distance between specimen in each well cell of a well plate disposed on the microscope stage and the objective lens is further increased in addition of the thickness of the stage heater. In this connection, it will be difficult or impossible to focus the objective lens on the specimen in each well cell, if as the microscope is a high-powered one. In other words, it will be difficult or impossible to focus the objective lens on specimen such as cells or microorganisms to be observed even if the objective lens is approached to its closet limit of the up-down or vertical direction (referred hereinafter to as z-direction). This is because the displace-able range of the objective lens in vertical direction is already be determined and limited on the basis of the microscope stage of a simple one-stage structure. Therefore, if the stage heater of the type above mentioned is simply incorporated into the movable type microscope stage, the objective lens can not be focused on specimen even under the approach-able limit. 
     Further, the condenser is also displaced relatively away from specimen to be observed because of the thickness of the movable type, three-stage microscope stage. In this connection, it will be difficult or impossible to focus light on the specimen to be observed, and, thus, sufficient amount of light may not be projected thereon. 
     In other words, the thickness of the movable microscope stage becomes large, the objective lens as well as the condenser is not approachable sufficiently to the specimen can, so that the objective lens as well as the condenser can not be bring closer to the specimen sufficiently to focus thereon. 
     It is an object of the present invention is to provide a microscope stage capable of always heating entire culture vessels such as well plates of various shapes or sizes, and capable of bringing the objective lens as well as the condenser closer to the specimen to be observed sufficiently to focus thereon even when the microscope is a high powered one. Further, it is another object of the present invention is to provide a microscope observing unit forming an enclosed space in combination with the drive base of the microscope stage, and capable of controlling atmosphere in temperature and/or humidity within the enclosed space. 
     SUMMARY 
     In accordance with the invention defined as a first aspect, there is provided a microscope stage comprising: a fixed base, a movable base on which a culture vessel accommodating an object to be observed is disposable, the movable base being movable relative to the fixed base in two-dimensional directions within a plane extending perpendicular to an optical axis of an objective lens, a shift means for shifting the movable base in two-dimensional directions, a light-transmittable portion for passing light, formed through the movable base with a size corresponding to an object-accommodating portion in the culture vessel, a stage heater provided on the fixed base for heating the entire culture vessel regardless of the two-dimensional displacement of the movable base, and a light-transmittable, circular portion of the stage heater for passing the light therethrough for making observation through the objective lens. 
     In accordance with the invention defined as a second aspect, there is provided the microscope stage according to the first aspect, wherein the circular portion of the stage heater for passing the light is provided opposite to a condenser of the microscope. 
     In accordance with the invention defined as a third aspect, there is provided the microscope stage according to the first or second aspect, wherein the light-transmittable portion of the movable base is an opening. 
     In accordance with the invention defined as a fourth aspect, there is provided the microscope stage according to the third aspect, wherein the size of an opening of the movable base corresponds to a two-dimensional maximum size of the culture vessel. 
     In accordance with the invention defined as a fifth aspect, there is provided the microscope stage according to the fourth aspect, further comprising an adapter adaptable within the opening of the movable base, the adapter being formed with an opening of a size corresponding to another small culture vessel. 
     In accordance with the invention defined as a sixth aspect, there is provided the microscope stage according to the fifth aspect, wherein the movable base includes a fixing means for securing the culture vessel of maximum size or the adapter in the opening of the movable base. 
     In accordance with the invention defined as a seventh aspect, there is provided the microscope stage according to any one of the first to sixth aspects, wherein the light transmittable, circular portion of the stage heater is a through hole. 
     In accordance with the invention defined as a eighth aspect, there is provided the microscope stage according to any one of the first to sixth aspects, wherein a heating section of the stage heater includes a transparent base plate and an electrically conductive transparent film. 
     In accordance with the invention defined as a ninth aspect, there is provided the microscope stage according to any one of the first to eighth aspects, wherein the movable base includes a lower base and an upper base, the lower base is linearly movable relative to the fixed base in a first direction, and the upper base is linearly movable relative to the lower base in a second direction perpendicular to the first direction. 
     In accordance with the invention defined as a tenth aspect, there is provided the microscope stage according to the ninth aspect, wherein the upper surface of the lower base is recessed to receive the upper base, and the lower surface of the lower base is recessed to receive the fixed base. 
     In accordance with the invention defined as a eleventh aspect, there is provided a microscope observing unit including; the microscope stage according to any one of the first to tenth aspects, a culture device disposed on the movable base to form an enclosed space in combination with the movable base, provided with a means for controlling the atmosphere of the enclosed space in temperature and humidity. 
     In accordance with the invention defined as a 12th aspect, there is provided the microscope observing unit according to the eleventh aspect, the culture device comprising: a housing adapted to be disposed on the movable base, and a top heater adapted to be disposed on the housing, wherein the top heater is provided with a heat producing portion covering over an upper opening of a housing, with a transparent base plate and an electrically conductive transparent film formed thereon. 
     In accordance with the invention defined as a 13th aspect, there is provided the microscope observing unit according to the 12th aspect, further comprising a spacer frame adapted to be interposed between the top heater and the housing for providing an additional height to the enclosed space in correspondence to the height of the culture vessel being used. 
     The microscope stage of the present invention is applicable to culture vessels, including well plates, of various shapes or sizes. The microscope stage of the present invention is capable of always heating the entire culture vessel. 
     The microscope stage has a structure capable of shifting the culture vessel disposed thereon in two-dimensional directions. The objective lens as well as the condenser can be brought closer to an object to be observed sufficiently to focus thereon even when the objective lens is one of high magnifying power. 
     Further, the microscope observing unit is capable of forming an enclosed space in combination with a movable base of the microscope stage, and capable of controlling the atmosphere within the enclosed space in temperature and/or humidity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described more fully with reference to accompanying drawings in which: 
         FIG. 1  is a perspective view illustrating a microscope to which the present invention is to be equipped; 
         FIG. 2(   a )-( d ) are perspective views illustrating various kinds of culture vessels for accommodating objects to be observed; 
         FIG. 3  is an exploded perspective view illustrating a microscope observing unit as an embodiment of the present invention, including a microscope stage and a culture device set on the stage; 
         FIG. 4  is an exploded perspective view illustrating the microscope stage as the embodiment; 
         FIG. 5  is a front view illustrating the microscope stage of  FIG. 4 ; 
         FIG. 6  is a side view illustrating the microscope stage of  FIG. 4 ; 
         FIG. 7  is a plan view illustrating the microscope stage of  FIG. 4 ; 
         FIG. 8  is a plan view illustrating the microscope observing unit in which a culture device is disposed on the microscope stage of  FIG. 4 ; 
         FIG. 9  is a cross-sectional view along the A-A line in  FIG. 8 ; 
         FIG. 10  is a cross-sectional view along the B-B line in  FIG. 8 ; 
         FIG. 11  is a perspective view illustrating a frame fixing means provided on a frame member; 
         FIG. 12  is a perspective view illustrating a well plate fixing means provided on the frame member; 
         FIG. 13  is a cross-sectional view illustrating a movable base after being displaced from a position as shown in  FIG. 9  in x-direction; 
         FIG. 14  is a cross-sectional view illustrating the drive base after being displaced from a position as shown in  FIG. 10  in y-direction; 
         FIG. 15  is a perspective view illustrating the frame member and an adapter for a dish; 
         FIG. 16  is a plan view illustrating the microscope observing unit in which the culture device is set on the stage with the adapter for the dish of  FIG. 15 ; 
         FIG. 17  is a plan view illustrating the microscope observing unit in which the culture device is set on the stage with the adapter for the well plate of  FIG. 2(   b ); 
         FIG. 18  is a perspective view illustrating a spacer; and 
         FIG. 19  is a cross-sectional view, corresponding to  FIG. 9 , illustrating the movable base in which the well plate of  FIG. 2(   d ) is contained in the enclosed space, which has been enlarged in its height with the spacer of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A best embodiment of a microscope observing unit including a microscope stage according to the present invention will now be described with reference to the attached drawings. 
     In the following description, a microscope to which the embodiment of the present invention is to be applied is described in summary, and then vessels for accommodating an object to be observed is described. The microscope stage and the microscope observing unit including the stage will then be described concretely. 
     A microscope  1  is provided with a microscope stage  25  of the present invention. Objectives  5  are attached to the end of body tubes  6  and disposed under the stage  25 . The three body tubes  6  and the objectives  5  attached thereto different in their magnifying power are supported by a revolving piece  8 . 
     The microscope  1  further includes binocular tubes  9 , eye pieces  11  attached to the tubes  9 , and a camera port  13  provided through a front, lower part of a body  7 . 
     Further, a penetrating illumination column  15  is provided on a rear, upper part of the body  7 . The column  15  supports a condenser  3  above the stage  25 . 
     As can be seen from the attached drawings, a microscope observing unit  31  according to the embodiment comprise the microscope stage  25  and a culture device  29  adapted to be disposed on the stage  25 . 
     Culture vessels of various configuration are illustrated in  FIGS. 2(   a )˜ 2 ( d ). 
     A dish  33  shown in  FIG. 2(   a ) is of transparent plastic material. The dish includes a shallow cylindrical body  33   a  and a lid  33   b  for covering the body  33   a . The diameter of the body  33   a  is about 35 mm, and the depth is about 10 mm. The dish is adapted to accommodate as one specimen cells and the like. 
     A well plate  35  shown in  FIG. 2(   b ) comprises a slide glass  35   a  and a frame member  35   b . The slide glass  35   a  has a width of about 75 mm, a length of about 25 mm, and a thickness of about 1 mm. The frame member  35   b  has a width of about 10 mm, a length of about 8 mm, and a depth of about 11.5 mm. The frame member  35   b  makes eight compartments  35   c  for accommodating specimens such as cells. 
     A well plate  37  shown in  FIG. 2(   c ) is of transparent plastic material, and includes a body  37   a  and a lid  37   b . The body  37   a  is a shallow container. The body  37   a  has a plurality of cylindrical compartments  37   c , each compartment  37   c  having a diameter of about 6.5 mm, and a depth of about 10.5 mm. In the body  37   a , the compartments  37   c  are aligned in 12 in the width direction and 8 in the longitudinal direction so that the total number of the compartments  37   c  is 96. The opened upper surface of the body  37   a  is adapted to be covered with the lid  37   b . The well plate  37  has, in the outer size, a width of about 127 mm, a length of about 85 mm, and the height of about 16 mm. 
     A well plate  39  shown in  FIG. 2(   d ) is of transparent plastic material, and includes a body  39   a  and a lid  39   b . The body  39   a  includes a plurality of cylindrical compartments  39   c . Each compartment  39   c  has a diameter of about 16 mm, and a depth of about 17 mm. In the body  39   a , the compartments  39   c  are aligned in 6 in the width direction and 4 in the longitudinal direction so that the total number of the compartments  39   c  is 24. The opened upper surface of the body  39   a  is adapted to be covered with the lid  39   a . The well plate  39  has, in the outer size, a width of about 127 mm, a length of about 85 mm, and the height of about 22.5 mm. 
     In the illustrated embodiments, the well plates  37  and  39  as shown in  FIGS. 2(   c ) and  2 ( d ) is a largest in the two-directions, and used one culture vessel. The dish  33  and the well plate  35  are used as other culture vessels on the stage with adapters  99 A and  99 B as mentioned herein below. The height of the well plate  39  is a largest among the culture vessels. 
     The microscope stage  25  will now be described in detail. 
     As shown in  FIGS. 3 and 4 , the microscope stage  25  includes a fixed base  47 , a movable base  49  which is adapted shift-ably in two-directions within a plane perpendicular to the optical axis of the objective  5 , a driving means for shifting the movable base  49  in two-directions, an opening  53  formed through the movable base  49 , and a stage heater  55  adapted to be mounted on the lower surface of the fixed base  47 . 
     The arrangement of the fixed base  47  and the stage heater  55  will now be described in detail. 
     The fixed base  47  may be a rectangular plate member through which a rectangular window  61  is provided for transmitting light therethrough. The stage heater  55  includes a rectangular heating section  58  containing heating wire (not shown) adapted to convert electricity to heat energy. The heating section  58  is protruding slightly upward. The heating section  58  is also provided with a circular opening  69  for transmitting light therethrough. The opening  69  is adapted to be positioned between and in opposite to the objective  5  and the condenser  3 . 
     The fixed base  47  is recessed on the lower surface thereof for accommodating the heating section  58 . The stage heater  55  is mounted on the lower surface of the fixed base  47  whereby the heating section  58  is adapted to the lower surface of the fixed base  47 . The central portion of the heating section  58  is exposed through the window  61 . The size and the shape of the heating section  58  is, as mentioned herein below, determined to cover the displacement range of the well plates  37  and  39  on the movable base  49 , so that the well plates  37  and  39  are always being heated nevertheless displacement of the movable base  49  on the stage  25 . 
     The arrangement of the movable base  49  will now be described in detail. 
     The movable base  49  includes a lower base  71  and an upper base  73 . The lower base  71  is provided with an upper surface recess  77  in which the upper base  73  is received. The lower base  71  is provided with a lower surface recess  79  in which the fixed base  47  is received. Therefore, this arrangement results in reduction substantially in the total thickness of the stage  25  relative to that of the existing movable stage. 
     As can be seen in  FIG. 6 , the lower base  71  is attached to the fixed base  47  via linear guide members  81 , so that the lower base  71  can shift linearly side to side direction (referred hereinafter to as x-direction). Further, as can be seen in  FIG. 5 , the upper base  73  is attached to the lower base  71  via linear guide members  83 , so that the upper base  73  can shift linearly back and force direction (referred hereinafter to as y-direction) in generally perpendicular to the x-direction. 
     The lower base  71  and the upper base  73  also have rectangular openings  53  for transmitting light therethrough. 
     The lower base  71  is provided on its lower surface with a rack  85 , and the upper base  73  is also provided on its lower surface with a rack  87 . 
     The upper base  73  is provided with a pinion mechanism  89  including pinions  92  and  94 . The pinion  92  is adapted to mesh with the rack  85  of the lower base  71 , and the pinion  94  is adapted to mesh with the rack  87  of the upper base  73 . Rotating a control knob  95  rotates the pinion  92 , and rotating a control knob  97  will rotate the pinion  94 . Thus, the pinion mechanism  89  and the racks  85  and  87  establish a driving means for shifting the movable base  49  in the two directions. 
     The movable base  49  further includes a vessel-keeping frame  74  for holding a vessel. The vessel-keeping frame  74  is adapted to be mounted in the opening  53 . The arrangement of the vessel-keeping frame  74  will now be described in detail. 
     A reference numeral  76  denotes a frame member having a rectangular opening  78  for transmitting light therethrough. As mentioned herein below, the opening  78  is of a size to accommodate all of the 96 compartments  37   c  when fitting the well plate  37  into the opening  78 . The opening  78  is also of a size to accommodate all of the 24 compartments  39   c  when fitting the well plate  39  into the opening  78 . An inwardly extending shelf-shaped portion  80  is formed in the lower end of the inner peripheral surface of the opening  78  of the frame member  76 . 
     At one of the corners of the frame member  76  is provided with a frame fixing means  135  comprising a corner block  103 , a coil spring  141  accommodated within the corner block  103 , a tongue  137  substantial part of which is accommodated within the corner block  103 , the remaining part protruding outwardly from the corner block  103 , and a detent (not shown) for preventing the tongue  137  from falling off from the corner block  103 . The tongue  137  is being urged by the coil spring  141  to protrude outwardly from the corner block  103 . 
     At the inner side of the corner block  103  is formed a cutout  104 . 
     At the corner opposite to that having the frame fixing means  135  is provide with a fixing means  101  for securing the well plate  37  or  39  comprising a corner block  102 , a coil spring  106  accommodated within the corner block  102 , a tongue  105  substantial part of which is accommodated within the corner block  102 , the remaining part protruding outwardly from the corner block  102 , and a detent (not shown) for preventing the tongue  105  from falling off from the corner block  102 . The tongue  105  is being urged by the coil spring  106  to protrude outwardly from the corner block  102 . At the tip of the tongue  105  is formed a recess  105   a.    
     At the inner side of the corner block  102  is formed a cutout  107 . The tip of the tongue  105  protrudes from the cutout  107 . 
     The well plate fixing means  101  are also used as a means for fixing the adapters  99 A,  99 B as mentioned herein below. 
     The microscope observing unit  31  is accomplished by setting a culture device  29  on the microscope stage  25 . 
     The culture device  29  will now be described in detail. 
     A reference numeral  109  denotes a housing in frame form. On the upper surface of the housing  109  is formed with a recess  109   a . A water tank  111  is also provided within the housing  109 . As can be seen from  FIG. 8 , the housing  109  is further provided with a water supplying tube  112 . The one end of the water supplying tube  112  is protruding into the water tank  111  and the other end of which is protruding outwardly from the outer surface of the housing  109  and connected to a water supplying conduit  119 . The housing  109  is also provided with a gas supplying tube  114 . The one end of the gas supplying tube  114  is protruding into the water tank  111  and the other end of which is protruding outwardly from the outer surface of the housing  109  and connected to a gas supplying conduit  121 . 
     A reference numeral  113  denotes a top heater to be placed on the housing  109 . The top heater  113  includes a supporting frame  63  and a transparent heater  64  formed by bonding a pair of glass plates by means of silicone resin. One glass plate is a base plate. On the other plate is formed a layer of electrically conductive transparent film. The top heater  113  can produce heat energy by supplying electric energy to the transparent film and converting electric energy to the heat energy. 
     A means for controlling the atmosphere in temperature and/or humidity of an enclosed space  115  includes the stage heater  55 , the top heater  113 , the gas supplying tube  114 , the gas supplying conduit  121 , the water supplying tube  112 , the water supplying conduit  119 , and a temperature sensor (not shown). 
     An adapter  99 A for the dish  33  is shown in  FIGS. 15 and 16 . 
     The adapter  99 A has a body  120  of a rectangular plate member of the same width and the same length as those of the well plate  37  or  39 . The thickness of the body  120  is about 3 mm. At the central portion of the body  120  is formed an opening  122 . The opening  122  has a circular portion of the size just to fit the body  33   a  of the dish  33  and rectangular portions extending in opposite x-directions from the circular portion. A pair of struts  128  extends from the body  120 . A presser plate  129  is supported pivotally on the end of each strut  128 . 
     An adapter  99 B for the well plate  35  is shown in  FIG. 17 . 
     The adapter  99 B has a body  140  of a rectangular plate member of the same width and the same length as those of the well plate  37  or  39 . The thickness of the body  140  is about 3 mm. At the central portion of the body  140  is formed an opening  142 . The opening  142  has a rectangular portion of the size just to fit the slide glass  35   a  of the well plate  35  and semi-circular portions extending in opposite y-directions from the rectangular portion. A strut  128  extends from the body  140 . A presser piece  129  is supported pivotally on the end of strut  128 . 
     A spacer frame  131  is shown in  FIGS. 18 and 19 . 
     The spacer frame  131  is incorporated when a relatively higher culture vessel such as the well plate  39  is used. 
     A body  131   a  of the spacer frame  131  has a fitting protrusion  131   b  on the lower surface thereof and a fitting recess  131   c  on the upper surface thereof. 
     Using method of the microscope stage  25  and the microscope observing unit  31  will now be described in detail. 
     The fixing base  47  is secured to the body  7  of the microscope  1  by means of bolts B, whereby the microscope stage  25  is attached to the microscope  1 . The vessel-keeping frame  74  is mounted in the opening  53 . When mounting the vessel-keeping frame  74 , the tongue  137  is being urged on the inner peripheral surface of the opening  53  against the coil spring  141  so that the frame  74  is be secured within the opening  53  without any play. 
     Subsequently, the well plate  37 , each compartment  37   c  of which is filled with a culture solution S and cells A to be observed, is mounted within the opening  78  of the vessel-keeping frame  74  and disposed on the inwardly extending shelf shaped portion  80  of the frame member  76 . When mounting the well plate  37 , one corner portion of the body  37   a  is fit into the recessed portion  105   a  of the tongue  105  of the well plate fixing means  101  to urge the tongue  105  into the corner block  102 . While keeping the condition, the body  37   a  of the well plate  37  is being fit into the opening  78 . The corner of the body  37   a  abuts the cutout  107  of the corner block  102  and the opposite corner thereof is fit within the cutout  104  of the corner block  103 . The body  37   a  is adapted to be urged onto the cutout  104  by means of the tongue  105  pushing the body  37   a  of the well plate  37 . Thus, the well plate  37  is secured within the vessel-keeping frame  74  without any play. 
     The housing  109  of the culture device  29  is then disposed on the upper base  73 . The housing  109  is adapted to be positioned to circumscribe the well plate  37 . The top heater  113  is disposed on the housing  109  to make the enclosed space  115  defined by the upper base  73 , the housing  109 , and the top heater  113 . 
     In order to increase the temperature of the enclosed space  115 , the heating section  58  of the stage heater  55  and the transparent heater  64  of the top heater  113  are switched on. The heat energy produced by the heating section  58  and the transparent heater  64  is controlled based on information from temperature sensors (not shown) so as to keep the temperature in the enclosed space  115  at a predetermined value. 
     Water is supplied within the water tank  111  from the water supplying means (not shown) through the water supplying conduit  119  and the water supplying tube  112 . The water is heated by the stage heater  55  and the top heater  113  and vaporized to achieve a predetermined humidity within the enclosed space  115 . 
     The enclosed space  115  is further filled with CO 2  gas delivered from the CO 2  tank (not shown) through the gas supplying conduit  121  and the gas supplying tube  114 . 
     Thus, the atmosphere within the enclosed space  115  in the temperature, the humidity, and the concentration of CO 2  is controlled to satisfy predetermined values, respectively. 
     When observing the cells A accommodated within the well plate  37 , the movable base  49  are shifted in the x-direction and/or the y-direction by manipulating the control knobs  95  and/or  97 . Thus, the cells A accommodated in the respective compartments  37   c  can be observed by shifting them to cross the optical axis L of the objective  5 . 
     In other words, the lower base  71 , together with the upper base  73 , is shifted from the position as shown in  FIG. 9  in the x-direction by turning the control knob  95  to rotate the pinion  92  to displace the rack  85 . In this connection the well plate  37  disposed on the upper base  73  is also be shifted in the x-direction as shown in  FIG. 13 . The upper base  73  is shifted from the position as shown in  FIG. 10  in the y-direction by turning the control knob  97  to rotate the pinion  94  to displace the rack  87 . In this connection the well plate  37  disposed on the upper base  73  is also shifted in the y-direction as shown in  FIG. 14 . 
     All the cells A accommodated within compartments  37   c  of the well plate  37  is always warmed nevertheless of whether the movable base  49  is shifted in any positions such as in  FIGS. 9 ,  13 ,  10 , and  14 , since the heating section  58  is of the size and the configuration sufficient to face with the well plate  37  disposed on the movable base  49 . 
     The objectives  5  can bring closer to the cells A than in the case of the microscope stage of the prior art since the thickness of the microscope stage  25  of the present invention is reduced substantially relative to the stage of the prior art. In this connection, the objectives of high magnifying power can be focused on the cells A. In addition, the condenser  3  can also bring closer to the cells A. This will allow the condensation of the sufficient amount of light onto the cells A. 
     When it is intended to make observation by using the dish  33  as shown in  FIGS. 15 and 16 , the adapter  99 A is attached to the vessel-keeping frame  74  in spite of the well plate  37 . The adapter  99 A is fit within the opening  78  and disposed on the inwardly extending shelf shaped portion  80  while urging the one corner portion of the adapter  99 A with the tongue  105 . The body  33   a  of the dish  33  filled with the cells A together with the culture solution, will then be fit within the opening  122  of the adapter  99 A, and be secured thereto by pivoting the pair of presser pieces  129  and elasticity urging the lid  33   b  of the dish  33  with them. 
     The method for operating the movable base  49  and the method for making observation of the cells A are the same as those used in the case of the well plate  37 . 
     When it is intended to make observation by using the well plate  35  as shown in  FIG. 17 , the adapter  99 B is attached to the vessel-keeping frame  74  in the same way as is used in the case of adapter  99 A. The well plate  35  is secured to the adapter  99 B by fitting the well plate  35  into the opening  142  and pressing and elasticity urging the slide glass  35   b  with the presser pieces  129 . 
     When it is intended to make observation by using the well plate  39  as shown in  FIG. 19 , the spacer frame  131  is interposed between the housing  109  and the top heater  113  with fitting the protrusion  131   b  formed on the lower surface of the spacer frame  131  into the recess  109   a  provided on the upper surface of the housing  109 . Thus, unintentional displacement of the spacer frame  131  from the housing  109  will be avoided. Further, the spacer frame  131  will provide an additional height to the enclosed space  115  for accommodating the well plate  39 . 
     When it is intended to employ a culture vessel higher than the well plate  39 , two or more spacer frames  131  can be stacked by fitting the protrusion  131   b  formed on the lower surface of the upper spacer frame  131  into the recess  131   c  formed on the upper surface of the lower one. Thus, unintentional displacement of the spacer frames  131  will be also avoided. 
     Although preferred embodiments of the present invention have been described, those of skill in the art will appreciate the variation and modification may be made without departing from the spirit and scope thereof as defined by appended claims. 
     For example, a microscope to which the microscope stage of the present invention is to be applied may not be limited to the inverted microscope  1 . The microscope stage of the present invention may also be applied to stereo microscopes and upright microscopes in which an objective is positioned above objects such as the cells A and a condenser is positioned below the cells A. 
     Light transmitting portion formed through the movable base  49  and formed through the stage heater  55  are not necessarily the opening  53  and the opening  69 , namely thought hole with no material, but also any transparent material such as a transparent glass plate may be used to cover the apertures. In the latter case, the transparent glass plate can be made of a transparent heater of the same structure as that of the top heater  113 . In other words, the heating section  58  of the stage heater  55  may be formed by such transparent heater. 
     As discussed hereinabove, the shape and the size of the opening  53  formed through the movable base  49 , the opening  78  of the vessel-keeping frame  74 , and the heating section  58  of the stage heater  55  is determined on the basis of the shape and the size of the well plates  37  and  39 . If it is intended to use a culture vessel of size larger than those of the well plates  37  and  39 , the shape and the size of the opening of the components of the microscope stage may be designed or determined on the basis of the shape and the size of the culture vessel. 
     Of course, the shape and the size of the adapters may be modified in dependent on the shape and the size of a culture vessel to be used. 
     The means for shifting or driving the movable base  49  is not limited to the control knobs  95  and  97 . The movable base  49  may be operated by servo or stepper motors. Further, ball and nut mechanism may be used instead of the rack and pinion mechanism.