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 
