56 INFECTION AND IMMUNITY. 



Data regarding the longevity of these organisms 

 in water and milk are given in the sections on 

 cholera and typhoid. 



"Water- "Water-borne" epidemics are characteristic in 

 B c'cmtaijt" this, that very many individuals are stricken sud- 

 Epidemics. ^ en jy an( j simultaneously and the outbreak is, at 

 first, limited to those who are supplied by the in- 

 fected water. "Contact" epidemics, on the other 

 hand, progress slowly and irregularly, although 

 they may finally reach large proportions. Nat- 

 urally an epidemic begun by contaminated water 

 may be maintained by contact, and continuance by 

 contact again offers opportunity for the fresh in- 

 fection of water, milk and food. The viability of 

 micro-organisms in the excreta, after the discharge 

 of the latter, is important, both from the stand- 

 point of water infection and that which occurs 

 by indirect contact. Uffelmann determined that 

 typhoid bacilli may live in the dejecta for many 

 months, and, at least under some conditions, the 

 cholera vibrios in the feces is viable for two or 

 three weeks (Lubarsch). 



conveyance As stated previously, diseases which are peculiar 

 by Food. f. Q marL ma y j^ Distributed by milk which has been 

 contaminated by convalescents (as in scarlet fever) 

 or by "carriers," or by some others indirectly from 

 these, or by infected water used in washing con- 

 tainers. Epidemics caused by infected milk are, 

 in miniature, similar to those arising from a con- 

 taminated water supply, their distribution coin- 

 ciding with the area of consumption of the milk. 



Other food substances act as carrying agents 

 only when they become infected accidentally, as by 

 flies, washing in contaminated water, or by con- 



