664 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



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 

 one authority for the statement that the internal organs of healthy 

 animals are sterile. This has been shown not to be the case universally. 

 Experiments have shown that fifty per cent of the internal organs of 

 rabbits, guinea-pigs, cats, dogs, mice, horses and cattle are not sterile. 

 Bact. tuberculosis has been found in absolutely normal human and 

 bovine lymph glands. The various pus-producing micrococci have 

 been frequently found in the spleen, kidney, liver, etc. Perhaps the 

 commonest group of bacteria to be isolated from the internal organs are 

 the intestinal forms. It has been demonstrated that intestinal micro- 

 organisms invade the tissues with surprising rapidity when for any 

 reason the resistance of the body is lowered. It has been noted also 

 that there are more bacteria in the internal organs of animals which 

 have been fasted than in those which have been fed. Peristaltic action 

 and the diffusion of food through the intestinal wall may be influencing 

 factors. The fact that the internal organs are not sterile in every case 

 is important as it may account for the so-called autogenic infections. 



THE MANNER IN WHICH INFECTIOUS AGENTS ENTER THE BODY AND 



THEIR SOURCES 



Air-borne Infections. The causal microorganisms of infectious 

 diseases are frequently excreted from the body of the diseased individual 

 and are deposited on the clothing, furnishings, on the floors and walls, 

 or on the ground. These microorganisms probably do not proliferate 

 except in rare instances, but frequently remain virulent for a short 

 period of time and are capable of being carried through the air for short 

 distances, producing in certain instances disease in other individuals. 

 There is no doubt that in diseases such as smallpox, measles, scarlet 

 fever and other acute exanthematous diseases together with such 

 diseases as plague and diphtheria, that the infectious agents may be 

 carried through the air after having been deposited on clothing and 

 furnishings. However, recent investigations have shown that this 

 method of transferring infection is comparatively rare and that most 

 infections are transmitted by direct contact. 



In the beginning it was supposed that the only way that bacteria 

 could be carried in the air was after having been dried on particles of 



