15 



Frozen Sections 



General Principles 



Nature of the Process 



The last three chapters have dealt with 

 sectioning specimens which have been 

 impregnated with some material to pro- 

 vide support, either through solidification 

 (wax) or through the evaporation of the 

 solvent (nitrocellulose). There are two 

 circumstances under which neither of 

 these processes may be used: first, when 

 it is desired to preserve in the tissues some 

 fatty material which would be dissolved 

 by the reagents used prior to wax impreg- 

 nation; second, when speed is of primary 

 importance, as in the productions of quick 

 sections from tumors for diagnostic pur- 

 poses. In both cases recourse may be had 

 to the method of frozen sections in which 

 material is rapidly frozen until it is of a 

 consistency which may be cut. Frozen sec- 

 tions should not, however, be employed 

 on any occasion when the normal processes 

 of embedding may be used. 



Choice of a Microtome 



Any of the microtomes previously dis- 

 cussed may be used for frozen sections 

 with the aid of special attachments. The 

 type of microtome shown in Fig. 84 is, 

 however, specially made for the purpose 

 and will be taken as the basis for the pres- 

 ent discussion. It is essential in cutting 

 •frozen sections that the knife should slice 

 rather than push, and this type of micro- 

 tome produces this movement without the 

 expensive sUding mechanism of the micro- 

 tome shown in Fig. 5G. The slicing effect is 

 produced by mounting the knife to swing 

 through the object when the handle on top 

 is turned. This type of microtome is not as 

 accurate, either as to. the thickness of sec- 



tion cut, or as to the repetition of this 

 thickness, as is the big shder; but it is pre- 

 sumed that no one would cut frozen sec- 

 tions if thickness and reproducibility were 

 primary objectives. The method of freez- 

 ing the object will be discussed after we 



ToCO^ 



CYUNDER^ 



Fig. 84. 



Spencer clinical microtome 

 fitted for freezing. 



liave dealt with the cjuestion of embedding 

 the material in a supporting substance. 



Choice of a Supporting Medium 



Biopsy material delivered to a tech- 

 nician from the operating theater is usu- 



157 



