98 PRINCIPLES OF VETERINARY SURGERY 



play the role of battling with the phagocytes while the 

 specific agent elaborates its toxin) are incapable of exhibit- 

 ing any pathogenic powers sufficient to overcome the resist- 

 ing forces of the body. Rogers has shown that it requires 

 a certain given number of tuberculous bacilli to kill a cavy 

 and analogous facts with other bacteria are legion. 



The channel of infection also has much to do with 

 determining the pathogenic quality of many bacteria. Mic- 

 robes that will produce pneumonia when introduced into 

 the lungs may cause but a local suppurating process when 

 inoculated elsewhere in the body. The bacillus mallei when 

 ingested or inhaled will produce an entirely dififerent clinical 

 tableau if inoculated into the skin. The bacillus tuberculosis 

 may cause consumption when inhaled. When ingested it 

 is capable of provoking entirely different localizations and 

 again, if inoculated directly into a trauma a still different pic- 

 ture is produced. Pyogenic cocci entering the umbilicus pro- 

 voke a grave polyarthritis and when injected- subcutaneously 

 a simple and even trivial abscess is the only result. These 

 examples might be enumerated in considerable numbers, 

 but the foregoing are sufficient to establish the fact that the 

 avenue of entrance is a marked determinating factor in re- 

 gard to the pathologic behavior of the disease producing 

 bacteria. 



Bacteria seem entirely incapable of traversing the 

 epithelial lining of the skin or mucous membranes, in the 

 absence of any breach of continuity. The skin or mucosae 

 must first be injured or diseased before the bacteria can 

 pass their protecting epithelial coating. A mere scratch of 

 a pin, a disturbed hair folhcle, a slight erosion of a mucous 

 membrane, trivial irritation, congestion or inflammation, or a 

 morbid process of whatever character is sufficient to admit 

 them. In a large percentage of instances the bacteria remain 

 quite persistently localized at the seat of infection or its im- 



