SECTIONING METHODS 



427 



the total tissue, which would include inactive material. Berenblum 

 et al. first removed lipid phosphorus by extracting with alcohol- 

 chloroform (3:1). Organic and inorganic acid-soluble phosphorus 

 was removed by extracting with 0.1 A^ hydrochloric acid; the tissue 

 was then ashed with perchloric acid, and the phosphorus in the ash 

 was measured. 



A. PREPARATION OF FROZEN TISSUE SECTIONS 

 OF ACCURATE THICKNESS 



In some instances it is undesirable to subject tissue to the em- 

 bedding process and the associated treatments with the various sol- 

 vents prior to the application of histochemical tests or analyses on 

 microtome sections. When this is the case, the freezing microtome 

 may be used for either fresh tissue or that fixed in a suitable man- 

 ner. It may be necessary to obtain sections of accurately uniform 

 volumes for quantitative work. The cross-sectional area of sections 

 can be controlled by punching out cylinders of tissue from frozen 

 material with metal borers of known internal diameters (Fig. 152). 



Fig. 152. Tissue borer and microtome cryostat. 

 From Linderstr077i-Lnng and Holler (1940) 



The cylinder of tissue can be placed on some wet filter paper set on 

 the freezing head of the microtome and then the whole firmly frozen 

 to the head. This is the procedure that has been followed in many 

 cases by the Carlsberg Laboratory investigators. They have found 

 too that a rotary microtome is less subject to factors which lead to 

 variations in thickness than the hand sliding type, and that the 



