BACILLUS TYPHOSUS. 415 
the milk cans were washed. A very alarming epidemic 
of typhoid developed, which was confined to the houses 
and asylums supplied with this milk. In our late war, 
not only water infection but food infection was notice- 
able, as in the case of a regiment where certain com- 
panies were badly infected, while others nearly escaped. 
Each company had its separate kitchen and food-supply, 
and much of the infection could be traced to the food. 
In this, as in all infectious diseases, individual sus- 
ceptibility plays an important role in the production of 
infection. Without a suitable soil upon which to grow 
the seed cannot thrive. There must in many be some 
disturbance of the digestion, excesses in drinking, etc., 
or a general weakening of the power of resistance of 
the individual, caused by bad food, exposure to heat, 
overexertion, etc., as with soldiers and prisoners, for 
example, to bring about the conditions suitable for the 
production of typhoid fever. 
The supposition that the breathing of noxious gases 
is conducive to the disease, though possibly true to a 
certain extent, as some animal experiments already 
referred to would seem to indicate, has not yet been 
conclusively proven; nor do Pettenkofer’s investiga- 
tions, into the relation of the frequency of typhoid 
fever to the ground-water level, satisfactorily explain 
the occurrencé of the disease in most cases, whether 
sporadically or in epidemics. 
Immunization. Specific immunization against experi- 
mental typhoid infection has been produced in mice, 
guinea-pigs, rabbits, dogs and other animals by the 
usual method of injecting at first small quantities of 
the living or dead typhoid culture and gradually in- 
creasing the dose. The blood-serum of animals thus 
