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XXVIII] Among those who ventured to formulate definite and more reasonable hypotheses, some considered that cholera, like the more familiar exanthematous fevers, was directly contagious. Others thought that it was not directly contagious, but that it was communicated by the evacuations of the sick after these evacuations had undergone some peculiar fermentation process outside the human body. Others again, as von Pettenkofer, regarded the virus as a chemical ferment which developed in the soil under certain unknown epidemic conditions.

Discovery of the comma bacillus* — Since the rise of the germ theory of infective disease most of these speculations have been definitely abandoned, or have received more precise expression in the view that cholera is caused by a certain bacterium, known as the comma bacillus or cholera vibrio, which Koch found to be present, practically invariably, in the stools and intestinal contents of cholera patients. This bacterium Koch first discovered in Egypt in 1883. Believing in its importance, he afterwards proceeded to India on a special mission, and there, in Calcutta, in 1884, he found the same bacterium in the intestinal contents of 42 fatal cases, and in the stools of 30 other cholera patients; in fact, he found it in every case of the disease examined. Moreover, he entirely failed to find it in any other disease or in healthy discharges. These observations, so far as they concern the presence of the comma bacillus in cholera stools, have been abundantly confirmed by many other workers; so that the presence or absence of this bacterium is now regarded as a trustworthy and valuable practical test of the choleraic or non-choleraic nature of any given case of intestinal flux; and this even by the opponents of Koch's special view as to the nature of the relationship of the bacterium in question to the disease with which it is so intimately associated. If only on account of its diagnostic value, the comma bacillus, therefore, is an organism of importance; but as many