EXAMINATION OF MICRO-ORGANISMS IN TISSUE 79 



ascertain their bearing towards the elements of the tissues, 

 and their exact situation in and between them. In par- 

 ticular, their physiological action, in spite of very advanced 

 methods of investigation, has not up to the present been 

 fully explained. When the microbes are present in masses 

 of considerable size, but only then, their position in the 

 tissues can be recognised in the simplest way in pieces of 

 the fresh organ by examining some of its tissue on a slide in 

 a drop of sterile water or salt solution. In the case of 

 fluids the addition of water may be omitted. The minute 

 elements are then examined with a high power (an oil- 

 immersion with Abbe's condenser and a diaphragm). We 

 cannot, however, ascertain by this method how the microbes 

 are related to the tissues, nor their exact situation in the 

 tissue and its elements. A small piece of it should there- 

 fore be torn up with needles and treated with a drop of 

 acid or caustic potash, so as to cause the connective tissue 

 which forms the bulk of organs to swell up. In this way 

 the bacteria, which exhibit greater power of resisting re- 

 agents, are brought out distinctly. Through the introduc- 

 tion of staining processes, however, methods have been 

 discovered which render it possible to demonstrate the 

 micro-organisms in uninjured tissue. 



Examination by the freezing method. — In order to be able 

 rapidly to examine pieces of organs, recourse is had to the 

 freezing microtome. The substance in the fresh state is laid 

 upon a roughened metal plate and frozen by means of an 

 ether spray apparatus. It is then cut into sections with a 

 cooled knife, and these are laid on slides, allowed to thaw, 

 and subjected to staining processes which will be described 

 later on ; after which they are most conveniently examined 

 in dilute glycerine. 



Hardening. — Owing to the frequent destruction of the 

 tissue in using the freezing microtome, caused by the 



