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 occurrence 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 



