SECTIONING 



275 



one end (bottom) of the celloidin block. The two are pressed 

 together; the celloidin at the junction is hardened in the air until it 

 is thick, then in the chlorofonn as before. 



SECTIONING. 



As soon as material is properly embedded one may proceed 

 directly to cutting sections for staining. ^Machines, called micro- 

 tomes (from the Greek, "to cut small"), have been devised and can 

 be regulated to cut sections of desired thickness easily and uni- 

 formly. Two general type^ of microtomes are in common use: 

 one, working on a rotary principle, is called a rotary microtome 

 (Fig. 163), and the other, cutting by sliding mo^'ements, is known 

 as the sliding microtome. The rotary type is suited for cutting 



Fig. 163.— Illustration of the rotary microtome. (Courtesy of Spencer Lens Co.) 



paraffin embedded material, while celloidin material is sectioned 

 with the sliding microtome, although the latter may be used for 

 paraffin material also. 



Rotary Microtomes and Paraffin Sections. — The illustration presents 

 the princij^al features of this tyi)e of microtome. The following 

 information should be sujjplemented by classroom demonstration 

 in the use of the machine and also by considerable actual experience 

 in section cutting by each student. Small metal discs or wooden 

 blocks are furnished to which the i)araffin block may be attached. 

 These supports can be then fastened into a holding device in the 

 microtome. 



We will suppose that we ha^•e a disc of paraffin containing three 

 pieces of embedded tissue. One of these is cut out of the disc bv 



