782 



MODE OF SPREAD OF INFECTIVE DISEASES. 



1. Contagious 

 obligatory 

 parasites with 

 slight resist- 

 ing power. 



With greater 



resisting 



power. 



2. Contagious 



facultative 



parasites. 



Spread of 

 anthrax. 



but this distinction is not of great importance from the 

 point of view of the mode of spread of human infective 

 diseases. 



To mention some examples, we have in the group 

 of the contagious obligatory parasites infective agents 

 which are distinguished by slight resisting power and 

 require direct inoculation ; for example, the agents of 

 syphilis, gonorrhoea, and hydrophobia. To those dis- 

 eases which can also be carried by various objects on 

 account of the greater resisting power of their causal 

 agents belong small-pox, measles, scarlatina, tuberculosis, 

 glanders, diphtheria, and the majority of the infective 

 diseases of wounds. Differences in the contagiousness 

 of these diseases are either due to the degree of resisting 

 power of the infective agents, or to the fact that the 

 situation of the points of invasion and the special protec- 

 tive arrangements of the healthy body only permit their 

 entrance in rare cases. 



To the group of the contagious facultative parasites 

 belong the exciting agents of typhoid fever, cholera, and 

 anthrax. Here also the chief mode of spread is by 

 means of surrounding objects, which only act as trans- 

 porting agents, viz., clothing, water, soil, &c. ; at times, 

 however, multiplication or fructification also occurs on 

 articles of food, in regions which are marshy, or where 

 vegetable remains are plentiful. &c. This occurrence 

 may exert a special influence on the mode of spread of 

 the disease, because the maintenance of the species is 

 thereby rendered certain for a considerable time, and 

 also because, as in the case of anthrax, the formation of 

 resisting spores occurs at times only outside the body. 



Anthrax behaves very differently according as it pursnos 

 the course of a septicasmia as a result of a cutaneous inocula- 

 tion, or of an intestinal anthrax from swallowing food con- 

 taining spores. In the first case, bacilli are not usually given 

 off from the affected body ; the surface of the wound is 

 occupied by other bacteria, and it is only at times that 

 anthrax bacilli are excreted in the urine; after death the 

 cadaver may become a prey to putrefactive bacteria without 

 the passage of virulent anthrax bacilli into the surroundings. 

 In such cases for example, in animals artificially inoculated 



