474 INFECTION AND IMMUNITY. 



lustrating this point was noted in the epidemic 

 which attacked Hamburg in 1892. In certain 

 streets in which the residents of the two sides ob- 

 tained their water supply from different sources, 

 one of which was infected, cholera was limited to 

 that side which was supplied with infected water. 

 Only irregular cases due to contact infection oc- 

 curred on the opposite side of the street. 



Epidemics which are due solely to contact infec- 

 tion develop slowly and irregularly. A common 

 incident is the successive involvement of the mem- 

 bers of a family, whereas others in the immediate 

 neighborhood are unaffected. Water-borne epi- 

 demics are invariably complicated by the occur- 

 rence of contact infection. The methods of con- 

 tact infection are not different from those men- 

 tioned under typhoid fever. Food or milk which 

 has been infected by contaminated water or by 

 other means may cause the development of isolated 

 groups or cases. 



Animals do not contract cholera under natural 

 Animals, conditions. By rendering the gastric contents of 

 guinea-pigs alkaline and introducing cultures into 

 the stomach through a tube, Koch induced a chol- 

 era-like process from which the animals died with- 

 in from twenty-four to thirty-six hours; an intra- 

 peritoneal injection of opium, to quiet peristalsis, 

 seemed to be necessary for the success of the ex- 

 periment. Similar results were obtained in very 

 young rabbits by feeding cultures to them (Issaeff 

 and Kolle, Metchnikoff). Guinea-pigs withstand 

 the subcutaneous inoculation of moderate amounts, 

 but are very susceptible to intraperitoneal inocula- 

 tion. Intravenous injections are exceedingly toxic 

 for rabbits, and a fatal cholera-like condition with 



