44 METHODS OF STUDYING MICROORGANISMS 



thin inverted glass (Fig. 14). He will discover from 

 this preparation under the microscope the presence of 

 motility and the manner of division of the bacteria. 

 From his tube cultures he chiefly finds out whether 

 the bacteria develop en/ymes. To the solid media 

 (agar-agar) he may add various sugars to discover the 

 fermentative powers of the bacterium. The fermenta- 

 tive powers may also be observed when the germs grow 

 upon bouillon containing the sugars. This broth is 

 placed in an apparatus called a fermentation tube so 

 arranged that the percentage of sugar broken up by 

 the bacteria can be estimated. When he shall have 

 made all his observations he will sum up his results 

 and identify according to the classification of bac- 

 teriologists. 



f^' ! .. .'"I: v'''^^-!^^..^^.!. *i '..., . .,. . I 



FIG. 14. Hollow slide with cover-glass. (Park.) 



The presence of bacteria is searched for in pus and 

 diseased tissues by making a smear from the fluid 

 or affected part upon glass slides and treating it with 

 certain dyes. Before the dyestuff is applied the smear 

 must be fixed by heat or alcohol or formaldehyde. 

 This is for the purpose of killing the albuminous 

 material, keeping it exactly as it was when removed 

 from the body, and rendering it susceptible of taking 

 up and permanently retaining stains, a property 

 living tissues and fluid possess to a very slight degree. 

 Once fixed and stained, examination will reveal the 

 bacteria present, and the observer can form an opinion 

 of the probable nature of the infection. Reference is 



