21 8 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



solid by the ether spray whilst the surgeon is removing- the 

 tumour; cut a suitable slice off the latter and place it on the 

 layer of ice thus formed ; direct the ethyl chloride spray down- 

 wards 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 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 para- 

 graph, 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 

 haematoxylin (with or without eosin as a counterstain) and 

 mounting in balsam. 



The requisites are : Five watch-glasses containing respec- 

 tively 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 i inch wide and 2 inches long*; 

 some needles, which may be mounted in handles; slides, 

 cover-glasses, and balsam. 



A section is to be removed from the bowl of water in which 

 it is floating by means of one of the strips of paper; this 

 must be inserted under it, and the section "pinned" in place 

 upon it by one of the needles. A special section-lifter may 



