PORTALS OF ENTRY OF INFECTIOUS AGENTS. 175 



conveyed from place to place in two shoes than in any 

 other way." Therefore, air-borne, as applied to a 

 disease, rather emphasizes the fact that the contagion 

 enters by way of the respiratory passages, than that it 

 is widely diffused in air. 



By the mouth and nose through air may 

 enter the infectious agents in small-pox, 



AND Nose ... ^ ^ r 



THROUGH chicken-pox, measles, scarlet fever, mumps. 

 Air. whooping-cough, pneumonia, tuberculosis, 



diphtheria, plague, anthrax, epidemic cere- 

 bro-spinal meningitis (?), rubella and influenza. 



A large number of the infectious and para- 

 MouTH gj|.j^ diseases are contracted exclusively 



P by the pathogenic agents entering the body 



Water. ^^ foods and water. This method of infec- 



tion is also by no means unusual in certain 

 diseases for which the respiratory passages are the ordi- 

 nary portals of entry. Foods and water, as a rule, offer 

 excellent pabula for infectious agents and parasites, 

 and are therefore quite frequently the means by which 

 diseases are spread. The pollution of drinking-water by 

 sewage, and the harm arising therefrom, has already 

 been considered. Foods in relation to disease, however, 

 requires some further elucidation; and while it is not 

 our aim to take up all foods which serve as vehicles for 

 infectious and parasitic agents, the manner of con- 

 tamination of some of those consumed daily will serve 

 to illustrate, in a general way, how these are a source of 



