PATHOGENIC BACTERIA OUTSIDE THE BODY 237 



called the carrier. Whenever, for any reason, the resistance 

 of an individual (see Chapters XXV et seq.) is lowered 

 either locally or generally some of these organisms are liable 

 to gain a foothold and cause infection. It sometimes 

 happens that a strain of dangerous organisms may be 

 developed in an individual in this way which is passed around 

 to others with its virulence increased and thus causes an 

 epidemic. Or, since all of the group are living under the 

 same conditions the resistance of all or many of them may 

 be lowered from the same general cause and an epidemic 

 result from the organism common to all (pneumonia after 

 measles, scarlet fever and influenza in camps). Protection 

 of the individual is chiefly a personal question, i. e., by 

 keeping up the "normal healthy tone" in all possible ways. 

 The use of protective vaccines (Chapter XXX) appears to 

 be advisable in such instances (colds, pneumonia after 

 measles and influenza, inflammation of throat and middle 

 ear following scarlet fever and measles). Results obtained 

 in this country during the recent influenza epidemic have 

 been conflicting, but, on the whole appear to show that 

 preventive vaccination against lyneumonia liable to folloto 

 should be practised. 



It w^ould seem that among groups of individuals where 

 infection may be expected the proper procedure would be 

 to prepare autogenous vaccines (Chapter XXX) from mem- 

 bers of the group and vaccinate all with the object of pro- 

 tecting them. 



II. B. {d) In this class come the "accidental carriers" 

 like flies, fleas, lice, bed-bugs, ticks and other biting and blood- 

 sucking insects, vultures, buzzards, foxes, rats and carrion- 

 eating animals generally; pet animals in the household, etc. 

 Here the animals are not susceptible to the given disease 

 but become contaminated with the organisms and then 

 through defilement of the food or drink or contact with 

 individuals or with utensils pass the organisms on to the 

 susceptible. Some biting and blood-sucking insects trans- 

 mit the organisms through biting infected and non-infected 

 animals successively. The spirilloses and trypanosomiases 

 seem to be transmitted in this way, though there is evidence 



