THE NATURAL HISTORY OF MAN 29 



the wholly parasitic and the mainly saprophytic 

 diseases, are a number of other zymotic diseases 

 which resemble contagious diseases on the one 

 hand, or malaria on the other, with respect to the 

 incapacity, or capacity, of their microbes to exist 

 apart from the human body. The microbes of 

 measles, consumption, chicken pox, scarlatina, 

 small-pox, influenza, etc., are all earth- or air-borne. 

 They are not communicated by direct contact, and 

 can therefore exist, at least for a limited time, away 

 from the human body ; but apparently they cannot 

 multiply in the outside world. The microbes of 

 cholera, enteric and yellow fevers, and some other 

 complaints, chiefly water-borne, are able not only 

 to exist outside the human body, but apparently can 

 increase and multiply away from it. But they 

 cannot thus multiply to an indefinite extent — at 

 any rate, they cannot to an indefinite extent 

 multiply away from water polluted by human filth, 

 for travellers in countries void of human inhabitants 

 are not infected by them. They are saprophytic to 

 a very limited extent only. 



it inhabits man. Dr Patrick Manson, whose researches in malaria 

 have been epoch-making, believes it is always parasitic. He thinks it 

 inhabits only man and the mosquito, passing from one to the other 

 and back again. It would be irrelevant to discuss the question here, 

 but I have given my reasons for dissenting from him elsewhere 

 {Physician and Surgeon, i2th April 1900). The important point for us 

 to note is 'Ca.^X, frotn whatever cause, malaria is confined to certain 

 localities. 



