588 PATHOGENIC MICROORGANISMS 



tion in man was followed by Metchnikoff, 1 who successfully produced 

 fatal disease in young suckling rabbits by contaminating the maternal 

 teat. 



Subcutaneous inoculation of moderate quantities of cholera spirilla 

 into rabbits and guinea-pigs rarely produces more than a temporary 

 illness. Intraperitoneal inoculation, if in proper quantities, generally 

 leads to death. It will be remembered that when working with intra- 

 peritoneal cholera inoculations the phenomenon of bacteriolysis was 

 discovered by Pfeiffer. 2 



Different strains of cholera spirilla vary greatly in their virulence. 

 The virulence of most of them, however, can be enhanced by repeated 

 passages through animals. Most of our domestic animals enjoy consid- 

 erable resistance against cholera infection, though under experimental 

 conditions successful inoculations upon dogs, cats, and mice have been 

 reported. Doves are entirely insusceptible. 3 



Hygienic Considerations. The cholera spirillum leaves the body of 

 the infected subject with the defecations only. Infection takes place, 

 so far as we know, only by way of the mouth. From these two facts it 

 follows that the chief source of danger for a community lies in infection 

 of its water supply. As a matter of fact the bacteria have been fre- 

 quently found in the wells, lakes, rivers, and harbors of afflicted terri- 

 tories, and in several cases it has been possible to define the limits of 

 an epidemic almost precisely by the distribution of the contaminated 

 water supply. A classic example of this is that of the Hamburg epi- 

 demic, during which Altona, a town as close to Hamburg as Brooklyn 

 is to New York, with unrestricted interurban traffic but with separate 

 water supply, was almost spared, while Hamburg itself was undergoing 

 one of the most virulent epidemics of its history. It has been statistically 

 noted, moreover, chiefly by Koch, that cholera in its spread not infre- 

 quently follows the water courses. Apart from infection through the 

 water supply, cholera may be transmitted directly or indirectly by con- 

 tact with contaminated linen, bedclothes, etc., the organism being con- 

 veyed to the mouth by the fingers, or by infected food. Epidemics due 

 to this mode of infection alone, however, are apt to be more narrowly 

 localized and more sporadic in their manifestations. It is probable that 

 this mode of infection is of great importance in countries where the disease 



1 Metchnikoff, Ann. d. 1'inst. Pasteur, 1894 and 1896. 



2 Pfeiffer, loc. cit. 



3 Pfeiffer und Nocht, Zeit. f. Hyg., vii, 1889. 



