INOCULATION OF ANIMALS. 415 



distance through the air, a conclusion which is well supported 

 by observations on the spread of the disease. Cholera is practi- 

 cally always transmitted by means of water or food contaminated 

 by the organism, and there is no doubt that contamination of 

 the water supply by choleraic discharges is the chief means by 

 which areas of population are rapidly infected. It has been 

 shown that if flies are fed on material containing cholera 

 organisms, the organisms may be found alive within their 

 bodies twenty-four hours afterwards. And further, Haffkine 

 found that sterilised milk might become contaminated with 

 cholera organisms, if kept in open jars to which flies had 

 free access, in a locality infected by cholera. It is quite 

 possible that infection may be carried "by this agency in some 

 cases. 



Experimental Inoculation. — In considering the effects of 

 inoculation with the cholera organism, we are met with the 

 difficulty that none of the lower animals, so far as is known, suf- 

 fer from the disease under natural conditions. Even in places 

 where cholera is endemic, no corresponding affection has been 

 observed in any animals. And further, before the discovery of 

 the cholera organism, various efforts had been made to induce 

 the disease in animals by feeding them with cholera dejecta, but 

 without success. It is therefore not surprising that the earlier 

 experiments on animals by feeding them with pure cultures were 

 attended with negative results. As the organisms are confined 

 to the alimentary tract in the natural disease, attempts to induce 

 their multiplication within the intestine of animals by artificially 

 arranging favouring conditions, have occupied a prominent place 

 in the experimental work. We shall give a short account of 

 such experiments. 



Nikati and Rietsch were the first to inject the organisms directly into the 

 duodenum of dogs and rabbits, and they succeeded in producing, in a con- 

 siderable proportion of the animals, a choleraic condition of the intestine ; in 

 their earlier experiments the common bile duct was ligatured, but the later 

 were performed without this operation. These experiments were confirmed 

 by other observers, including Koch. Thinking that probably the spirillum, 

 when introduced by the mouth, is destroyed by the action of the hydrochloric 

 acid of the gastric secretion, Koch first neutralised this acidity by adminis- 

 tering to guinea-pigs 5 c.c. of a 5 per cent solution of carbonate of soda, and 

 some time afterwards introduced a pure culture into the stomach by means of 

 a tube. Of nineteen animals treated in this way, only one died with choleraic 



