414 BACTERIOLOGY. 



seven years after the original infection. There is no 

 reason to deny that such opportunities for a latent ex- 

 istence of the typhoid bacillus may not occur outside 

 of the body. Indeed, many epidemics of typhoid 

 fever can only be accounted for by some such assump- 

 tion of latency in or outside of the body. 



The bacilli may reach the mouth by means of infected 

 fingers or articles of various kinds, or by the ingestion 

 of infected food, milk, water, etc., or by more obscure 

 ways, such as the contamination of food by flies and 

 other insects, or by the inhalation through the mouth 

 of dust containing typhoid bacilli. Of the greatest 

 importance, however, is the production of infection 

 by contaminated drinking-water or through drinking- 

 water or milk, which is the most plausible explana- 

 tion for the majority of epidemics of typhoid fever. 

 In many cases indirect proof of this mode of infec- 

 tion has been found in the known contamination of 

 the water with typhoid feces or urine, and in some few 

 cases it has been confirmed by direct proof in finding 

 the bacilli. Examples of infection from water and 

 milk have come frequently under our direct observa- 

 tion for instance, a large force of workmen obtained 

 their drinking-water from a well very near to their 

 work. Typhoid fever broke out, and continued to 

 spread until the well was filled up. Investigation 

 showed that some of the sick, before their discovery, 

 repeatedly infected the soil surrounding the well with 

 their urine and feces. Another instance of milk in- 

 fection secondary to water infection was the case of a 

 milk dealer whose son came home suffering from 

 typhoid fever. The intestinal movements were thrown 

 into a small stream which ran into a pond from which 



