Making Sections 



165 



Fig. 128. Applying Anderson's medium to tissue about to be frozen. 



be made to cut sections much less than 20 fi in thickness by this method, 

 and often sections of 30 p are sufficienlty good for diagnostic purposes. 

 It is then only necessary to continue to pull the handle until the object 

 starts to cut, while observing the nature of the sections. If the sections 

 crumble under the action of the knife, while the gum melts instantly on 

 contact with it, it may be presumed that the block has not been frozen 

 sufficiently hard; the carbon dioxide may again be turned on for a few 

 moments, and another cut taken. It will only take a moment or two to 

 establish the optimum condition under which only slightly curled sec- 

 tions appear on the blade of the knife. As the blade, however, is likely to 

 have become soiled, it is now washed with a drop of warm water to re- 

 move the dried gum and then used to cut as many sections as are re- 

 quired. As each section is cut, it must be removed from the blade of the 

 knife to the dish of 70 per cent alcohol shown in the figure. The majority 

 of people working under pressure use their little finger (Fig. 129) for 

 the removal of the section, although a number of very competent techni- 

 cians prefer to use a brush for this purpose. As soon as the section has 

 been removed, it is transferred to the 70 per cent alcohol, where the gum 

 will soon be dissolved. 



Cutting without support is much more difficult and should be confined 

 to homogeneous blocks of tissue. In this case the tissue, either fresh or 

 fixed in formaldehyde, is trimmed so that a straight edge will be opposed 



