MICROSCOPICAL EXAMINATION OF BACTERIA. 47 



sterilised needle to a drop of sterilised water on 

 a slide, thinning it out, and covering with a 

 cover-glass as already described. A more satis- 

 factory method, by which one can keep micro- 

 organisms under observation and study their 

 movements, spore-formation, etc., will be described 

 under " Drop-cultures. " Tissues in the fresh state 

 may be teased out with needles in sterilised salt 

 solution, and pressed out into a sufficiently thin 

 layer between the slide and cover-glass. Glycerine 

 may in many cases be substituted for salt solution, 

 especially for the examination of micro-organisms 

 such as Actinomyces, Aspergilli, etc. 



There is as a rule no difficulty in recognising 

 the larger micro-organisms such as those just 

 mentioned, but where we have to deal with very 

 small bacilli, bacteria and micrococci, they may 

 possibly be mistaken for granular detritus or fat- 

 crystals, or vice-versa. They are distinguished by 

 the fact that fatty and albuminous granules are 

 altered or dispersed by acetic acid, and changed by 

 solution of potash ; alcohol, chloroform, and ether 

 dissolve out fat crystals or fatty particles ; on the 

 other hand, micro-organisms remain unaffected by 

 these re-agents. This micro-chemical reaction is 

 made the basis of Baumgarten's method (p. 278). 



