592 BACTERIOLOGY. 



Water. — Quantitative analysis requires more care in 

 fciie measurement of the exact volume of water em- 

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

 iiumber 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 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 diiferent 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 babteria 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 — i. e., if they are 

 growing or dying. Represent the results graphically, 

 and it will be noticed that in many cases there is 

 during the first three or four days a multiplication, 

 after which there is a rapid diminution; and, if the 

 organism does not form spores, usually death in from 

 ten to twelve days. This is not true for all organisms, 

 but does hold for many. 



"Where it is not convenient, however, to make the 

 analysis on the spot, the sample of water should be 

 taken and packed in ice and kept on ice until the plates 



