CHAPTER XVIII. 



CHOLERA. 



Introductory. It is no exaggeration of the facts to say that 

 previously to 1883 practically nothing of value was known re- 

 garding the nature of the virus of cholera. In that year Koch 

 was sent to Egypt, where the disease had broken out, in charge 

 of a commission for the purpose of investigating its nature. 

 In the course of his researches he discovered the organism 

 now generally known as the comma bacillus or the cholera 

 spirillum. Further observations carried out in nearly a hundred 

 cases, chiefly in India, convinced him of the constant presence 

 of this organism in cholera and of its causal relationship to the 

 disease. He also obtained pure cultures of the organism from a 

 large number of cases of cholera, and described their characters. 

 The results of his researches were given at the first Cholera 

 Conference at Berlin in 1884. The general conclusions at 

 which Koch arrived received, in the main, confirmation from 

 the investigations of others, though some criticism arose, espe- 

 cially as regards the uniformity of the characters of the cholera 

 spirillum. 



Since Koch's discovery, and especially during the epidemic 

 in Europe in 1892-93, spirilla have been cultivated from cases 

 of cholera in a great many different localities, and though this 

 extensive investigation has revealed the invariable presence in 

 true cholera of organisms resembling more or less closely Koch's 

 spirillum, certain difficulties have arisen. For it has been found 

 that the cultures obtained from different places have shown 

 considerable variations in their characters, and, further, spirilla 

 which closely resemble Koch's cholera spirillum have been cul- 

 tivated from sources other than cases of true cholera. There 

 has therefore been much controversy, on the one hand, as to the 

 signification of these variations whether they constitute differ- 

 ent species, or whether they are to be regarded as indicating 



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