EXAMINATION OF WATER 705 



number more constant, while in very impure water the 

 number may diminish. It is essential, therefore, if 

 reliable results are to be obtained, for the specimen to be 

 examined at once (within three hours). If this cannot be 

 done the specimen should be packed in ice ; the cold 

 will then inhibit multiplication to any extent. Special 

 double-chambered metal boxes are made for this 

 purpose : the bottle containing the sample is placed in 

 the inner chamber, the outer chamber (which surrounds 

 the inner) being filled with a mixture of ice and sawdust, 

 and the whole is packed in a wooden box with felt lining. 

 The addition of 10 per cent, of common salt to the sample 

 has been stated to preserve the original bacterial content 

 of the water unaltered up to -ninety-six hours after taking 

 the sample, without icing, but Raju and Fox find it unre- 

 liable. Besides the sample packed in ice, a " Winchester 

 quart ' ' of the water may also be collected for examination 

 for the spores of the B. Welchii group. 



The routine bacteriological examination of the speci- 

 men may be carried out according to the following 

 scheme (here somewhat modified) drawn up by com- 

 mittees of the Royal Institute of Public Health : 1 



PROCEDURES. The following procedures should be 

 carried out : 



(a) Enumeration of the organisms which will develop 

 aerobically in gelatin at 20 C. 



(6) Enumeration of the organisms which will develop 

 aerobically in agar at 37 C. (Enumeration is carried out 

 by counting the number of colonies which develop in the 

 plates [see below].) 



(c) Search for Bacillus coli, and identification and 

 enumeration of this organism if present. 



(d) Search for, and enumeration of, streptococci. 



As a routine measure it is not necessary to search for 



1 Journ. State Med., vol. xii, 1901, p. 471, and vol. xxii, 1914, p. 558. 

 M.V. 45 



