METHODS AND CHANNELS OF INFECTION 663 



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 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, Bact. influenzae, Bact. 

 tuberculosis, M. intracellularis 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 exceedingly interest- 

 ing to note that Bact. tuberculosis and Bact. diphtheria, 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, 

 epidemic meningitis, typhoid, Asiatic cholera and dysentery "bacillus 



