A New Freezing Mierotome. 



187 



by means of forceps until the paraffin becomes sufficiently hard. 

 In order that the paraffin may fairly support the tissue it is necessary 



Fig. 2. 



Vertical section of the Microtome. — The hole (A) is shown containing a piece 

 of tissue, and the freezing box containing a freezing mixture. K, a movable 

 bottom to the hole (A). R, Transverse section of the knife employed in making 

 the sections. Other letters as in Fig. 1. 



that the surface of the latter be dry. This is easily accomplished 

 by leaving it exposed to the air for some time, either with or without 

 previous immersion in spmt. A mixture of equal parts of beeswax 

 and olive oil is much recommended for the same purpose as the 

 paraffin in the above case. No doubt the wax and oil mixture is most 

 excellent for imbedding tissues, and it can be cut with the gi-eatest 

 ease. But it melts at a higher temperature than paraffin, and, 

 owing to the great thermal expansion, it retracts from the side of 

 the tube of the machine, and so the wax cylinder becomes loose. 

 The only way in which this can be prevented is by heating the 

 machine to a like temperature before putting the wax into it. 

 This is tedious ; and inasmuch as it is unnecessary in the case of 

 paraffin, this is to be preferred. Even with this, however, the 

 paraffin cyhnder is apt to become a little loose, and to turn round 

 in the machine : hence it is important that there be an eccentric 

 hole in the brass plug (K, Fig. 2), so that the paraffin may pass 

 into the hole, and thereby be prevented from rotating. When the 

 machine is used for the second object — that is, for freezing — the 

 following directions are to be attended to : — Surround the freezing 

 box with two or three layers of flannel, and screw the machine to a 

 table. Unscrew the movable bottom or plug (K, Fig. 2), and pour 

 methylated spirit into the tube (C) ; oil the side of the plug ; 



VOL. X. Q 



