154 AIDS TO BACTERIOLOGY 



Transmission of the disease may take place by means 

 of water (as at Hamburg), by milk (rare), uncooked 

 vegetables, or by fomites. The infection is confined to 

 the bowel and stomach discharges, and is not found in 

 the urine. 



During outbreaks of cholera a number of persons show- 

 ing only slight or no symptoms get infected at the same 

 time as those who fall ill, and harbour the organism for 

 some time. Haffkine has proved that such * vibrio- 

 carriers ' can spread the disease. 



As the vibrio offers little resistance to drying, it seems 

 unlikely to be disseminated by dust. At the same time, 

 it is readily capable of a saprophytic existence. Un- 

 cultivated vibrios die more speedily than cultivated 

 ones and the duration of their life is shorter in the hot 

 season than in the cold (Greig). 



In some waters the cholera vibrio will live for consider- 

 able periods (see p. 225). Charcoal filters, once infected, 

 have been known to continuously pollute water otherwise 

 pure for many weeks, and cause grave epidemics. 



The best-known instance of milk infection is that of the 

 outbreak of cholera in the Gaya Gaol, in which it was 

 surmised that flies carried the infection. 



Under ordinary conditions, little or no toxin is found in 

 cultures, but a powerful toxin (presumed to be an endo- 

 toxin) has been obtained by disintegration of the vibrionic 

 structure. 



Vaccine. Haffkine's vaccine is prophylactic, not 

 curative. An attenuated vaccine (prepared from cholera 

 spirilla grown on agar at 38 or 39 C., over the surface 

 of which a current of moist sterile air is passed) is injected. 

 Five days later a stronger (' exalted ') vaccine is ad- 

 ministered, which does not exert its full power of immuni- 

 sation till five days after inoculation. The virulence of 

 the latter is obtained by passage through the peritoneal 

 cavities of guinea-pigs. Both inoculations are made 

 subcutaneously. Neither vaccine is sterilised or filtered, 

 both living bacilli and their products being injected. 

 The protection is of a very decided character. 



Treatment by antisera has met with little success. 

 The cholera immune serum is bacteriolytic, not antitoxic. 



