OCCURRENCE OF VIBRIOS 439 



Metchnikoff x ascribes the immunity of animals to intes- 

 tinal cholera as largely due to the inhibitory action of 

 the other organisms present in the digestive tract. In 

 man digestive disturbances are often an important pre- 

 disposing cause of an attack. The acidity of the gastric 

 juice is also probably a means of defence (see " Water "). 



The blood-serum of an animal immunised by injections 

 of the cholera vibrio gives a typical agglutination reaction 

 with recent cultures of the organism. The reaction can 

 also be obtained with the blood-serum of cholera patients, 

 sometimes as early as the first day of the disease, but it is 

 usually of little use for diagnostic purposes, as the disease 

 generally runs such a rapid course. 



Occurrence of the vibrio. That the cholera vibrio is 

 etiologically associated with the disease seems to be 

 beyond any doubt, and so constant is its presence in true 

 cholera that all investigators, even those who at one time 

 opposed Koch's views, rely on its detection for the bac- 

 teriological diagnosis. The matter, however, has become 

 complicated owing to the detection in various natural 

 waters of pathogenic vibrios which, although not identical 

 with the cholera vibrio of Koch, resemble it so closely that 

 it is difficult to classify them as anything but varieties 

 of the cholera vibrio. In certain epidemics in India varia- 

 tions have also been noted in the cholera vibrios that have 

 been isolated. Sanarelli 2 isolated from the Seine and 

 Marne thirty-two vibrios, of which four were almost indis- 

 tinguishable from cholera, except that they were only 

 slightly pathogenic, but by passage through a series of 

 animals their pathogenic power was much enhanced. 

 Sanarelli believed that these were the descendants of true 

 cholera vibrios that had gained access to the rivers during 

 some previous epidemic of cholera. At the same time it is 



1 Ann. dc I Inst. Pasteur, vii, pp. 403, 562 ; vol. viii, pp. 257, 520. 



2 Ibid, vii, p. 693, and ix, p. 129. 



