BACTERIA IN WATER 65 



as final tests as to whether or not the organism is B. coli, for 

 unfortunately some members of the family do not show each 

 of these three features. Most varieties, however, appear 

 to show some motility, a small number of flagella, a typical 

 growth on potato, and develop more rapidly on all media 

 than B. typhosus. These characters, plus one or more of 

 the three features above named, are diagnostic data upon 

 which reliance may be placed. 



Cholera. This word is used to cover more a group of dis- 

 eases rather than one specific well-restricted disease. In recent 

 years it has become customary to speak of Asiatic cholera 

 and British cholera, as if indeed they were two quite different 

 diseases. But, as a matter of fact, we know too little as yet 

 concerning either form to dogmatise on the matter. Until 

 1884 practically nothing was known about the etiology of 

 cholera. In that year, however, Koch greatly added to our 

 knowledge by isolating a spirillum from the intestine and in 

 the dejecta of persons suffering from the disease. 



Cholera has its home in the delta of the Ganges. From 

 this endemic area it spreads in epidemics to various parts of 

 the world, often following lines of communication. It is a 

 disease which is characterised by acute intestinal irritation, 

 manifesting itself by profuse diarrhoea and general systemic 

 collapse, with cramps, cardiac depression, and subnormal 

 temperature. The incubation period varies from only a few 

 hours to several days. In the intestine, and setting up its 

 pathological condition, are the specific bacteria ; in the 

 general circulation their toxic products, bringing about the 

 systemic changes. Cholera is generally conveyed by means 

 of water. 



The spirillum of Asiatic cholera (Koch, 1884) generally 

 appears, in the body and in artificial culture, broken into 

 elements known as " commas." These are curved rods with 

 round ends, showing an almost equal diameter throughout, 

 and sometimes united in pairs or even a chain (spirillum). 



