448 BACTERIOLOGY. 



is then placed in the incubator at 37 to 38 C., for 

 thirty-six to forty-eight hours, after which plates are 

 to 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 temperature 

 upon the bacteria of water, Dr. Yaughan, 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 BACTEKIA IN 

 WATER. Quantitative analysis requires more care in 

 the measurement of the exact volume of water employed, 

 for the results are to be expressed in terms of the num- 

 ber 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 would 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- 



