BACTERIOLOGICAL STUDY OF WATER. 493 



be made from it in the usual way; the results will often 

 be a pure culture of some single organism, either one of 

 the intestinal variety or a closely allied species. By a 

 method analogous to the latter the spirillum of Asiatic 

 cholera has been isolated from water; and by taking 

 advantage of the effect of elevated temjierature ujjou 

 the bacteria of water Dr. Vaughau, of Michigan, has 

 succeeded in isolating from suspicious waters a group of 

 organisms very closely allied to the bacillus of typhoid 

 fever. 



The Quantitative Estimation of Bacteria in 

 AYater. — Quantitative analysis requires more care in 

 the measurement of the exact volume of water em- 

 ployed, for the results are to be expressed in terms of the 

 number of individual organisms to a definite volume. 

 The necessity for making the plates at the place at 

 which the sample is collected is to be particularly 

 accentuated in this analysis, for the multiplication of 

 the organisms during transit is so great that the results 

 of analyses made after the water has been in a vessel 

 for a day or two are often very different from those that 

 w ould have been obtained on the spot. 



Note. — Inoculate a tube containing about ten cubic 

 centimetres of sterilized distilled or tap water with a 

 very small quantity of a solid culture of some one of 

 the organisms with which you have been working, 

 taking care that none of the culture medium is intro- 

 duced into the water-tube and that the bacteria are 

 evenly distributed through it. Make plates at once, 

 and on each succeeding day, from this tube, and deter- 

 mine by counts whether there is an increase or diminu- 

 tion in the number of organisms — /. e., if they are 



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