740 MODE OF SPREAD OF INFECTIVE DISEASES. 



diseased 



3. Transport 



4. Transport 



5. Transport 

 J 



Influence of 



contagious- 



noss 



contact with the fresh or dried morbid excreta, or with 

 ol) J ects contaminated therewith, the contact being 

 brought about by intentionally handling these materials, 

 by bites, &c. 



3. By insects which transport fresh or dried excreta, 

 or objects contaminated with them, to individuals capable 

 of taking the infection. 



4. By swallowing food or water which contain infec- 

 ^ ve g erms - This is the most important mode of trans- 

 port for those infective diseases in which the invasion 

 only begins from the intestine (typhoid fever, cholera). 

 Water and food may be directly contaminated by the 

 infected excreta, or the contamination in the case of the 

 food may be occasioned by contact, insects, adhering 

 portions of soil, or infective air germs, in the case of 

 water by the wash linen, &c. 



5. By aerial germs. As has been pointed out above, 

 the transport by currents of air only occurs in the case 

 of those infective agents which can withstand drying. 

 Accordingly it does not come into play in cholera; it is, 

 further, almost excluded or occurs very rarely in glanders 

 and some infective diseases of wounds ; on the other 

 hand it plays an important role in the acute exanthe- 

 mata, typhus, typhoid fever, tuberculosis. 



It is apparent that the last-mentioned mode of trans- 

 P ort h as an important influence on the mode of con- 

 tagion. In cases where it cannot occur the other modes 

 of transport are much more easy of recognition and 

 avoidance. We can comparatively readily protect our- 

 selves against infection by contact by means of careful 

 cleanliness, and against the introduction of the infec- 

 tive agents by food and water, by careful selection and 

 preparation of the nutriment, and direct transport by 

 infected animals or insects occurs on the whole very 

 seldom. On the other hand, transmission by currents 

 of air occurs in an unnoticeable manner and one against 

 which no protection exists, and it may extend over 

 considerable distances ; the infective agents which are 

 transportable in this way may also infect individuals 

 who do not come into immediate contact with the sick 



