Cutting 



FROZEN SECTIONS 



159 



could be frozen by this means almost as 

 rapidly as witl: carl)()n dioxide. The stench 

 and fire hazard which accompany this 

 procedure, however, limit it to those who 

 do not have access to carbon-dioxide 

 cylinders. 



Process of Cutting 



The prime necessity for jjroducinfj; a 

 good section is, of course, a sliarp micro- 



assumed that a carbon-dioxide cylinder 

 has been attached to the tube leading to 

 the microtome, and that a brief trial has 

 shown the gas to be flowing satisfactoi'ily. 

 Pick up with the pi])et about half a 

 cubic centimeter of tlio syrup, place this 

 on the freezing table of the microtome, 

 and turn on a small jet of carbon dioxide. 

 Within a moment or two the gum will con- 

 geal and the cai'bon dioxide mav be tui'ned 



Fig. 86. Removing section from Icnife. 



tome knife. The nature, care, and sharpen- 

 ing of microtome knives has already been 

 discussed in Chapter 12. It may be pointed 

 out here, however, that no provision is 

 made for altering the cutting angle of the 

 knife in most freezing microtomes, there- 

 fore, a knife, which is intended for use 

 with a given microtome should be secured 

 from the manufacturer. 



Let us assume that we have slightly 

 more than the minimum time, and that a 

 section is to be made with the syrup of 

 Anderson. Before cutting, set out a bottle 

 of this syrup, a pipet of the eye-dropper 

 type, and a jar of 70% alcohol in which to 

 receive the sections as they are cut. It is 



off. The object to be sectioned is then 

 (Fig. 85) placed on top of this congealed 

 layer of gum, and more gum is poured over 

 the surface. Care must be taken that there 

 is a layer of uncongealed gum l>eneath the 

 object or it may loosen. Turn on the 

 carbon dioxide and, as soon as the gum 

 covering the object is congeahng, pour on 

 a little more gum so that the object be- 

 comes thoroughly covered. Next, turn off 

 the carbon dioxide and insert the knife. 

 Take an experimental cut across the top 

 of the material and continue to shave it 

 down with the thickness control set at 

 40 microns until the specimen is reached. 

 Now reset the thickness control. No at- 



