184 CLINICAL BACTERIOLOGY AND HiEMATOLOGY 



The mass must not be frozen too hard ; if this has been the 

 case, the necessary thawing will be hastened by grtitly breathing 

 on the block. If it thaws too much, a few squeezes of the bellows 

 will bring it to the proper consistency. 



For extremely rapid work, the best method of freezing is by the 

 use of liquid carbon dioxide : this, however, is difficult in private 

 practice, owing to the unportability of the cylinders. The best 

 method is to use ethyl chloride or an^stile in metal cylinders, 

 such as are used for local anaesthesia. The best method is as 

 follows : Place a few drops of water on the plate of the microtome, 

 and freeze it solid by the ether spray whilst the surgeon is 

 removing^ the tumour ; cut a suitable slice oif the latter and place 

 it on the layer of ice thus formed ; direct the ethyl chloride spray 

 downwards on to the slice, which will be frozen in a few seconds. 

 Unless the water be previously frozen on the plate of the microtome 

 the block of tissue is very liable to slip, the lower portion being 

 frozen last. 



Where very rapid work is required it is not advisable to stain 

 the sections in the method described in the next paragraph, since 

 it takes too long. A simple stain (such as watery methylene blue) 

 is used, the staining being done on the slide, a cover-glass applied, 

 and the excess of stain removed by means of blotting-paper. It 

 is necessary to acquire a considerable amount of experience of 

 this method before using it for diagnosis, as the appearance 

 of sections prepared in this way and examined in a watery fluid is 

 very different from that which they have when double-stained and 

 mounted in balsam. 



STAINING AND MOUNTING FROZEN SECTIONS 



These processes are best carried out in watch-glasses. No 

 attempt will be made to describe the methods by which frozen 

 sections may be stained for the purpose of bacteriological research, 

 for they are not so suitable as paraffin sections for this purpose. 

 We shall describe the process of staining in hsematoxylin (with or 

 without eosin as a counterstain) and mounting in balsam. 



The requisites are : Five watch-glasses containing respectively 

 haematoxylin, watery solution of eosin (about i per cent.), alcohol 

 (50 per cent.), absolute alcohol, and clove oil ; a saucer or other 

 vessel containing water to which a few drops of ammonia have 

 been added ; several strips of thin writing-paper, each about 



