THE MICROVIVISECTION METHOD. 



127 



stage. This is in order to enable one to use a moist chamber of 

 the minimum height (see below). 



An important factor in the manufacture of the microdissection 

 instrument is that the two horizontal movements run true and 

 keep the needle point always in the same plane. Otherwise, at a 

 critical moment in the dissection, a reversal of a horizontal screw 

 may either suddenly lower the needle-point out of focus or jam 

 it against the coverslip and break it. Unfortunately, the last 

 model put out by the University of Kansas is deficient in this 

 respect. The existence of lost motion in the screws can be taken 

 care of in the manipulation but if the needle tip does not run true 

 in a horizontal plane the peace of mind of the operator may be 



sorely tried! 



THE MOIST CHAMBER. 



The moist chamber (Fig. 3) is a glass slide to which are ce- 

 mented strips of glass in such a way as to form a box open at the 

 top and at one end. For cement Canada balsam may be used. 



FIG. 3. Moist chamber for microdissection. 



A shallow trough, to hold water, is made with a narrow glass 

 strip set across the floor of the chamber 8 or 9 mm. from the 

 closed end. This and other small strips set outside the chamber 

 serve to reinforce the walls. Care must be taken that the upper 

 edges of the chamber be even and level when placed on the stage 

 of the microscope. A carefully grease-free cleaned coverslip 

 with a hanging drop containing the objects to be dissected forms 

 the roof of the chamber. The roof is sealed on with vaseline 

 smeared along the upper edges of the walls of the chamber. 



The height of the chamber is conditioned by the focal distance 

 of the condenser used and by the minimum working room that 



