METHODS AND CHANNELS OF INFECTION. 523 



testinal tract of persons suffering from or convalescent from the fever. 

 The same is true with the majority of the causal microorganisms. 

 There are some microbic agents, however, which exist in the soil but 

 probably do not undergo multiplication such as the B. tetani, of tetanus 

 or lockjaw, Bact. welchii, of emphysematous or gaseous gangrene, and 

 the B. botulinus, of meat poisoning. These bacteria sometimes exist 

 in the intestinal tracts of animals such as the horse and in all probability 

 their occurrence in the soil is due to their deposition in manure. 



THE OCCURRENCE or PATHOGENIC MICROBIC AGENTS UPON AND IN 

 THE BODIES or HEALTHY ANIMALS AND MAN. 



The exposure to the air of the external surfaces of the body makes 

 it especially easy for microorganisms to collect upon them. The 

 large percentage of the microorganisms which collect on the external 

 surfaces are non-pathogenic but there are frequently disease-producing 

 ones among them. The various varieties of the M. pyogenes are almost 

 universally present on the skin and also on the exposed mucous mem- 

 branes. Strept. pyogenes, Bact. influenza, Bact. tuberculosis, M. intracellu- 

 laris var. meningitidis, Strept. pneumonia, Bact. diphtheria and many other 

 species may be present. The mouth and nose are excellent places for 

 microorganisms to collect and excellent for their growth as the requisite 

 conditions such as food, heat and moisture are present. It has been stated 

 on competent authority that all the species of bacteria which have been 

 described as occurring in various parts of the body have also been found 

 in the mouth. These bacteria do not necessarily produce disease or injure 

 the body unless the vitality is lowered and they enter into the tissues. 

 They feed upon the desquamating cells and the excretions. It is exceed- 

 ingly interesting to note that Bact. tuberculosis and Bact. diphtheria, 

 as before stated, have been found in the nose of persons who have never 

 had these diseases. These bacteria have also been shown to be virulent 

 and such persons are somewhat dangerous to other more susceptible 

 persons. It is also frequently noted that pathogens are found in the 

 bodies of persons after they have recovered from the disease and 

 that these individuals disseminate the microorganisms and infect non- 

 immune individuals. This may be the case in typhoid fever, Asiatic 

 cholera and dysentery. 



In regard to the occurrence of microbic agents in the internal organs 



