METHODS AND CHANNELS OF INFECTION 663 



isms. 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, Bad. welchii of emphysematous or gaseous gangrene, 

 and l;he B. botuUnus of meat poisoning. These bacteria sometimes 

 exist in the intestinal tracts of animals such as the horse and in all prob- 

 ability their occurrence in the soil is due to their deposition in manulre. 



The Occurrence of Pathogenic Microbic Agents Upon and In 

 THE Bodies of Healthy Animals and Man 



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

 course, 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 dis- 

 ease-producing ones among them. The various varieties of the M. 

 pyogenes are almost universally present on the skin and also on the 

 exposed mucous membranes. Strept. pyogenes, Bad. influenza, Bad. 

 tuberculosis, M. intracellularis var. meningitidis, Strept. pneumoniee, 

 Bad. 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 prodtice 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 exceedingly interest- 1 

 ing to note that Bact. tuberculosis and Bact. diphtherice, as before stated, 

 have been found in the nose of persons who have never had these dis- 

 eases. These bacteria have also been shown to be virulent and 

 undoubtedly such persons are extremely 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 dis- 

 ease and that these individuals disseminate the microorganisms and 

 infect non-immune individuals. This may be the case in diphtheria, 

 typhoid, Asiatic cholera and dysentery "bacillus carriers." 



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

 of the body the following may be said. For a long time it was claimed 

 that the internal organs of man and animals were sterile. Neisser is 



