SECTION THREE 



Technique: 



1. Pieces of tissue are fixed in the usual manner. 



2. Wash in running water for the prescribed time for the parti- 

 cular fixative employed. If a fixative containing mercury has been 

 used, remove mercurial precipitate by the standard technique. 



3. Immerse the tissue in two changes of Pyridin, from two to 

 eight hours in each, according to the nature and the thickness of 

 the tissue. 



4. Immerse for twenty-four hours each in two changes of a 

 mixture consisting of equal volumes of Pyridin and 4% Celloidin 

 (formula as above). 



5. Immerse in 8% Celloidin for twelve hours. 



6. The tissue is then removed from the Celloidin bath, blocked 

 and cut into sections by the standard technique described on 

 pages 487-9. 



FROZEN SECTIONS 



For the identification of fat in tissues ; for certain impreg- 

 nation methods for the central nervous system ; and for the 

 rapid examination of pathological material, such as pieces 

 of tumour, which may be sectioned, stained and diagnosed 

 within a few minutes of their removal by the surgeon in 



the operating theatre 



Sections as thin as 5/^ may be cut, and an advantage of this 

 method is that there is a lesser degree of shrinkage than in the case 

 of paraffin-embedded material. It is not, however, possible to cut 

 serial sections by this method, and sections cannot be stored before 

 staining as in the case of paraffin-embedded material. Frozen sec- 

 tions should be employed only for the specific purposes mentioned 

 above and not as an alternative to paraffin embedding. It should 

 be noted that frozen sections are manipulated in the same way as 

 Celloidin sections, but greater care must be exercised on account 

 of the absence of any embedding mass. 



Tissues should not be frozen too hard or the sections will curl 

 up and split. 



A special microtome is required for cutting frozen sections. 



491 



