METHODS AND CHANNELS OF INFECTION .. 673 



is rapidly fatal. Just so with the Strept. pyogenes, depending on 

 whether it enters the circulation, the Ijonphatic vessels of the skin or 

 the connective tissues there results septicemia, erysipelas, or abscesses 

 which obviously differ in their severity. The same is true of practically 

 all the pathogenic bacteria which invade the plant and animal body, 

 the variation in the route produces a great variation in the type and 

 the results of the infection. 



It was mentioned in the beginning of this discussion that infection 

 included certain things such as the entrance of bacteria into the body 

 tissues, their increase and their injury to the body. There is some 

 variation in what constitutes an infection depending upon the infectious 

 rnicroorganism and the tissue it attacks. For example, Msp. comma 

 of Asiatic cholera does not produce an infection unless it comes into 

 contact with the intestinal mucosa and in this case it does not enter 

 the tissues but sets up an inflammatory process on the surface. If 

 this same bacterium comes into contact with tissues such as those of 

 the nose, throat, lungs, no infection results. In the case of B. typhosus 

 of t)T)hoid fever the bacterium not only attacks the intestinal mucosa, 

 but in addition it enters the tissue of the lymphatic patches and sets 

 up an inflammation. This microorganism may also invade the 

 circulatory system directly. In order for such an organism as the 

 Strept. pneumonitB to produce pneximonia it is only necessary for the 

 bacteria to come into contact with the thin, single-celled, alveolar wall 

 through the blood or air passages. In case this bacterium produces an 

 abscess it is necessary for it to first enter into the tissues. In the 

 pneumonic form of plague, although infection is supposed to be ac- 

 compKshed generally by the inhalation of bacilli, the Bact. pestis may 

 be carried to the alveolus through the circulation and thus enters the 

 tissues of the lung before actually invading the alveoli. This some- 

 times occurs in case of Strept. pneumoniae. It also gives rise to abscesses 

 occasionally but only when it invades lymphatic glands. The same is 

 true of the large number of infectious microbic agents; there is a varia- 

 tion in the infection due to the variation in the microorganism and 

 the point where this agent attacks the body. The severity of an 

 infection, as for example, a pneumonia due to Strept. pneumonia or 

 to Strept. pyogenes, or to Bact. pneumonice (Friedlander) or to Bact: 

 pestis, would vary with the infectious agent, its virulence and number, 

 and with the resistance of the individual infected. 

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