41 6 BACTERIOLOGICAL ANALYSES 



ably ' 'sterile" medium; plate or tube cultures should be 

 made from the various diluting fluids; every tube of 

 carbohydrate medium that is inoculated should go 

 into the incubator in company with a similar but un- 

 inoculated tube, and so on. 



BACTERIOLOGICAL EXAMINATION OF WATER. 



The bacteria present in the water may comprise 

 not only varieties which have their normal habitat in 

 the water and will consequently develop at 20 C., but 

 also if the water has been contaminated with excremen- 

 tal matter, varieties which have been derived from, or 

 are pathogenic for, the animal body, and which will only 

 develop well at a temperature of 37 C. In order to 

 demonstrate the presence of each of these classes it will 

 be necessary to incubate the various cultivations at 

 each of these temperatures. 



Further, the sample of water may contain moulds, 

 yeasts, or torulas, and the development of these will be 

 best secured by plating in wort gelatine and incubat- 

 ing at 20 C. 



1. Quantitative. 



Collection of the Sample. The most suitable vessels 

 for the reception of the water sample are small glass 

 bottles, 60 c.c. capacity, with narrow necks and over- 

 hanging glass stoppers (to prevent contamination of 

 the bottle necks by falling dust). These must be 

 carefully sterilised in the hot-air steriliser (vide page 



(a) If the sample is obtained from a tap or pipe, 

 turn on the water and allow it to run for a few minutes. 

 Remove the stopper from the bottle and retain it in 

 the hand whilst the water is allowed to run into the 

 bottle and three parts fill it. Replace the stopper and 

 tie it down, but do not seal it. 



(b) If the sample is obtained from a stream, tank, 



