106 PRINCIPLES OF VETERINARY SURGERY 



and various alkaline and saccharine mixtures are also used 

 for special purposes. 



In addition to these media, all of which must be prepared 

 with due respect to certain rules, there are others which are 

 required to meet the peculiar demands of certain bacteria. A 

 detailed description of the preparation of culture media can- 

 not be undertaken here. The reader is referred to works 

 on bacteriology, which cover the essential details. 



MICROSCOPIC EXAMINATION OF BACTERIA. 



When it is possible the bacteria should be examined 

 in the living state, which then reveals their actual shape, 

 size, motility and grouping. When a complicated process 

 of preparation is found necessary, as is often the case, the 

 bacterium may present a totally imnatural appearance. Dry- 

 ing, fixing, boiling, steaming and staining, although abso- 

 lutely necessary processes of preparation in many instances 

 are capable of giving an entirely wrong impression of the 

 real appearance of any given bacterium. When these pre- 

 paratory steps are used, due allowance must always be made 

 for the changes they are certain to bring about. 



The simplest microscopic examination of bacteria is ac- 

 complished by placing a drop of the culture on the slide, 

 covering it with the cover-glass and then focusing tlie in- 

 strument upon it. This method answers only for immediate 

 examination ; the evaporation of the solution destroys it for 

 further use. The one chief objection to this simple process 

 is that the movement of the fluid under the cover-glass 

 might be mistaken for the motility of bacteria. 



The hanging-drop is by far the best method of micro- 

 scopical examination of bacteria. By this method they are 

 actually observed in their natural abode. They can be ex- 

 amined as regards shape, size, motility, grouping, fission, 

 tporulation with the greatest accuracy, and for several days 



