194 



PRACTICAL MICROSCOPY. 



In working, place in the freezing box alternate layers of 

 finely powdered ice and common salt, taking care that they 

 are pushed well round the tube of the machine ; attach an 

 indiarubber tube to H and conduct the water into a jar or 

 pail, seeing also that it is kept open in order that the liquid 

 may find easy egress. The mixture of ice and salt must 

 be added at intervals, and the contents of the box stirred 

 occasionally with a short rod in order to promote the 

 escape of fluid. 



FIG. 181. 



The gum solution is run into the well of the microtome 

 and covered with a piece of guttapercha ; when the film of 

 ice has formed at its periphery, the tissue should be held 

 against the advancing film until it becomes fixed in 

 position for easy section. The razor used should be of 

 the form already described (R, Fig. 181), and when in 



