CHAPTER XII 



PREPARATION OF SECTIONS BY FREEZING 



TECHNIQUE 



223. The preparation of sections by freezing with CO2 gas is 

 now a positive and indispensable method used in laboratories 

 where experimental work is carried out, and in pathological and 

 surgical institutions where rapid diagnosis is necessary. This 

 method has a number of important advantages, two of which are 

 that the time ordinarily taken in imbedding in paraffin wax or 

 other masses is saved, and that first contact of tissues with fixing 

 fluids may be avoided. Serial sections cannot be prepared by 

 this method, though with great experience something approaching 

 this may be achieved. The possibilities of the frozen section 

 are not yet realised in zoological laboratories and the method 

 should be of great use to cytologists. In microchemical technique 

 the frozen sectioning microtome is indispensable. 



In the older models of this microtome, ether was used for 

 freezing, and it was usual to soak the pieces for some hours in 

 gum, dextrine or sugar solutions to prevent ice crystals forming. 

 In the most modern technique, made possible by the use of COj 

 jets on the microtome knife, the sections are stuck upon the slide 

 by means of their own albuminous (proteid) juices, and no water 

 is used until after the sections have been fixed in osmic or formalin 

 vapour. 



It is believed by some workers that frozen sections are not fit 

 for the best cytological study. This is wrong, for sections made 

 by this method and stained by Hollande's chloro-carmine method, 

 for example, can be extremely delicate and beautiful. 



224. Freezing Microtomes. A number of firms make admirable 

 microtomes, but, if possible, an instrument witli a knife cooling attach- 

 ment should be purchased. This is necessary for the best type of work. 



FROZEN SECTIONS 



225. Preparation of Material. Material may be cut fresh or 

 after fixation. In the latter case any of the usual fixatives, 

 such as Zenker, formalin 10 per cent., Bouin, etc., are suitable. 

 For quick surgical diagnosis 40 per cent, formaldehyde is generally 

 used, small pieces of tissue being put in the fluid until they are 

 penetrated and sink. Tissues containing much fat will not sink 



120 



