CHAPTER V 



IDENTIFICATION OF BACTERIA— GENERAL 



PRINCIPLES 



When examining morbid material or blood for bacteria, 

 it does not follow that because microscopical examination 

 fails to reveal them that they are absent. They may be 

 so few in number as to escape notice, or the material 

 examined may not possess any bacteria in that particular 

 sample. This is commonly seen in tuberculosis of the 

 udder, where the milk may be centrifugalized and yet no 

 bacilli are revealed. Again, in abscess formations the 

 digesting influence of the purulent matter may be so 

 pronounced that the active organisms are only to be found 

 in the cyst wall or its neighbourhood. Moreover, it is 

 well to be careful in forming an opinion of the presence 

 of bacteria taken from animal discharges after dissolution, 

 for extraneous contamination rapidly takes place from the 

 air or from the intestines. In the case of an animal dying 

 from anthrax, for example, we know how rapidly the blood 

 becomes contaminated with putrefactive organisms from 

 the intestines after death, thereby adding greatly to the 

 difficulty of arriving at an accurate diagnosis. 



Hanging- Drop Preparations. 



Hanging -drop preparations are used principally to 

 identify the motility or otherwise of bacteria, and also 

 to observe their growth and development. Hollow-ground 



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