100 PRINCIPLES OF VETERINARY SURGERY 



nitrogen from the air and combining it into compounds 

 useful for both vegetable and animal life. 



Many micro-organisms have the property of peptonizing 

 the casein of milk. Some digest casein without changing 

 the appearance of the milk, some coagulate it, some gelatin- 

 ize it, while still others reduce it to a watery fluid. (More 

 extensive works on bacteriology must be consulted for a 

 more comprehensive study of these functions.) 



The bacteria belonging to each of these classes may or 

 may not produce disease, which fact, in the study of pathol- 

 ogy, necessitates the division of all bacterial forms into two 

 great classes, viz., (i) Pathogenic bacteria, or those which 

 produce disease, and (2) non-pathogenic bacteria, or those 

 which do not produce disease. 



According to the oxygen required for their growth, 

 micro-organisms are divided into three important groups : 

 aerobic bacteria, anaerobic bacteria, and facultative anaer- 

 obic bacteria. It must be remembered that all micro-organ- 

 isms require oxygen for their propagation. Oxygen is 

 indispensable to all living things, and the bacterial forms 

 are no exception. This classification refers to the require- 

 ment of free oxygen only. 



Aerobic bacteria include all those forms that will thrive 

 in the presence of free, uncombined oxygen atoms. Exam- 

 ples, bacillus tuberculosis, bacillus diphtherias, bacillus sub- 

 tilis, etc. 



Anaerobic bacteria include all those forms which cannot 

 thrive or even grow in the presence of free oxygen. To 

 these micro-organisms free oxygen is a deadly poison, and 

 will either destroy them or prevent their successful reproduc- 

 tion. Examples, bacillus of Nicolaier, septic vibrion, bacil- 

 lus butyricus, etc. 



Facultative bacteria, facultative-anaerobic bacteria or 



