290 



SECTIONING 



[ CH. X 



The tissue is held by the microtome and moved up by means of a 

 screw. The knife rests on the top of the microtome and is moved 

 across the tissue by the hand. Microtomes of this kind are excel- 

 lent. No one need wait for expensive automatic microtomes to do 

 good sectioning. With a good table microtome the knife being 

 guided by the hand or hands of the operator, he can make straight 

 cuts as for paraffin sectioning, or drawing cuts as for collodion work. 

 (Figs. 228-229). 



FIG. 228 FIG. 229 



FIGS. 228-229. Hand and table microtomes. Both have a screw f 01 ele- 

 vating the object to be cut and a surface on which to rest the section knife. 

 228 in held in the hand, 229 is fastened to a table. The knife is held and moved 

 by the hand in both cases. ( Cuts loaned by the Bauch & Lomb Optical Co) . 



438. Sectioning with a Freezing Microtome. In this 

 .method of sectioning the tissue is rendered firm by freezing and the 

 sections are cut rapidly by a planing motion as with paraffin. Now 

 the most usual freezing microtome is one in which the freezing is 

 done with escaping liquid carbon dioxid. The microtome is in 

 general like the one shown in Fig. 229. The knife should be very 

 rigid. A plane blade is often made use of. The tissue may be 

 either fresh or fixed. If alcohol has been used it must be soaked 

 out of the tissue by placing it in water. Sometimes tissues are 



