278 



TECHNIQUE 



to melt, and the ribbons may become attached to the Iwttom of the 

 receptacle in which they are stored. 



The Sliding Microtome and Celloidin Sections. The accompanying 

 illustration presents an idea of a present-day example of the sliding 

 microtome. (Fig. 165.) The knife is mounted in a holder that 

 fits over the smooth surface of the sliding device. The position 

 of the knife may be fixed by the screws that clamp down on the 

 handle. The fiber block with the attached celloidin block con- 

 taining the embedded tissue is fastened into the clamp at one 



Fig. 165.— Illustration of a sliding microtome. (Courtesy of Spencer Lens Co.) 



side of the slide over which the knife is carried. The clamp holding 

 the embedded block is connected with a device which is essentially 

 a fine-threaded screw to which a micrometer is attached. When 

 the micrometer disc is properly turned a certain distance, the screw 

 lifts up the embedded block a certain definite distance above the 

 cutting edge of the knife. The knife must be arranged at an 

 oblique angle with the line of the slide carriage. Both knife and 

 embedded block are kept moistened with 70 per cent alcohol through 

 the sectioning process. The knife is drawn past the celloidin block 

 with the right hand. One can determine by means of the micro- 

 meter disc how far to turn the screw, and so determine the thickness 



