228 PRACTICAL NOTES OX HISTOLOGY. 



The jar should be lifted from time to time, to permit of the 

 partial removal of the gaseous alcohol and ether. The time the 

 mass is required to remain under the jar depends much on the 

 temperature of the room, and varies from one to six days. On 

 account of size it is easier to cut the eye into pieces about quarter 

 inch thick, and afterwards cut in the microtome. If the division 

 is done before embedding, the lens will be displaced. When eyes 

 are exceedingly large, and embedding is thus made difficult, 

 re-embed one of these slices and so obtain a requisite degree of 

 hardness. 



Sections may be cut in three ways : — 



(a) By freezing microtome. 



(/3) By any slide microtome, as Jung's. 



(r) By a microtome arranged that sections may be cut under 

 spirit. 



(a) Place mass in water for from six to twenty-four hours, until 

 nearly all the spirit has been removed. Place in gum for a couple 

 of hours or more, then freeze, cut and float off the knife in hot 

 distilled water in a capsule. If all the spirit has been removed 

 from the mass, the celloidin, when frozen, often becomes intensely 

 hard and difficult to cut. This is readily obviated by placing the 

 knife in warm water before cutting the sections. 



(/3 or y) Fix the mass firmly to a cork-covered plate. This is 

 always difficult to do unless there is one flat surface to the 

 celloidin. The most rapid method of fixing is to moisten the 

 cork and the flat surface of celloidin with ether, and to firmly 

 press the moistened surfaces against one another for five to ten 

 minutes ; the ether has then evaporated, and the celloidin 

 adheres firmly to the cork. Another way is to smear some thick 

 solution of celloidin over both surfaces, to press them together for 

 fifteen to thirty minutes, then to place them in alcohol for twenty- 

 four hours. There are also other methods for securing the mass, 

 with gelatine or with paraffin, but the two described are rather 

 more simple. The sections should always be manipulated 

 between two pieces of tissue paper, since any rough usage causes 

 displacement. The freezing method is used for all sections, but 

 to some workers, in cases of large sections, cutting under spirit 

 is preferred. The section must be thoroughly dehydrated by long 



