40 MANUAL OF EQUINE MEDICINE. 



Very small variations in the composition of the food 

 material may favour the development of one form rather 

 than another. 



As an example of this, it is noteworthy that Koch was 

 unable to inoculate a field-mouse with organisms which 

 always produced fatal septicaemia in a house-mouse. A 

 similar difference may exist between two animals exposed 

 to the action of a specific virus, when one of them is in- 

 fected while the other escapes. Thus a very slight change 

 in the system, or in part of it, may enable organisms to 

 grow in it, though previously unable to do so. 



Pasteur has divided Bacteria into serobious and ansero- 

 bious, according as they require for life free oxygen or not. 

 The Bacillus Anthracis dies in the absence of free oxygen. 

 Bacterium Termo and the yeast-plant can live with or with- 

 out it. For Bacillus Septicaemia of rabbits, air is not only 

 unnecessary but even fatal (Pasteur). 



Temperature. — Each organism flourishes best at a special 

 temperature. In some, as in Bacillus Tuberculosis, the 

 range within which growth can take place is very limited ; 

 in others, the range is much greater. 



The reproduction of Bacteria ceases at 5° C, and that of 

 many at a much higher temperature, but death does not of 

 necessity ensue. 



Some are said to resist the greatest degrees of cold, and 

 the spores of Bacillus Anthracis have been exposed to 

 — 140° C. without manifest injury. 



Dry spores of Bacillus Anthracis are able to resist ex- 

 posure to a temperature of 140° C. for over two hours. 



Boiling, and even a much lower temperature than 100° C, 

 will kill many forms. Boiling for one or two hours will 

 destroy all non-spore-bearing organisms, but solutions con. 

 taining spores will not be sterilized unless the exposure to 

 this heat is continued for many hours. 



