PATHOGENIC BACTERIA 269 



These few experiments show that the internal resistance of 

 the body is greater against some infecting organisms than 

 others. There is, however, a limit to the number of micro- 

 organisms which may be introduced into the body without 

 producing any pathological condition. 



It should be remembered that the phagocytes of the body 

 aid materially in combating infections. They are able to 

 destroy only certain species of bacteria and certain numbers 

 of bacteria, without the body becoming infected. It will be 

 readily seen, therefore, that the number of bacteria influences 

 and modifies the infection. 



(3) The Avenue of Infection. By this expression is meant 

 the point and channel of infection. It makes a decided difference 

 in the symptomatology and subsequent results if the avenue 

 of infection differs when a definite microorganism is the eti- 

 ological factor. For example, Bact. tuberculosis when enter- 

 ing the body through the respiratory or digestive tract may 

 produce tuberculosis of the lungs or tuberculosis of the in- 

 testines and accessory organs -and, furthermore, usually ter- 

 minates fatally. If Bact. tuberculosis infects the skin, a dis- 

 tinctly local disease known as lupus results which may per- 

 sist indefinitely without ending fatally. The Str. pyogenes 

 when it enters the superficial tissue of the body produces 

 erysipelas and abscesses, and, when present in the circulatory 

 system, produces septicemia. M. pneumonias may produce 

 pneumonia, abscesses, conjunctivitis, otitis, and meningitis, 

 depending upon its point of entrance and the tissue attacked. 



