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BACTERIOLOGICAL, EXAMINATION OF 

 WATER. 



The water to be examined must be received in a 

 sterilized bottle or flask, thoroughly protected against 

 subsequent contamination. Furthermore, in view of the 

 rapid multiplication of bacteria, a given sample of water 

 should be examined as soon as possible after collection. 

 The method commonly employed consists in the deter- 

 mination of the number of bacteria present in a given 

 volume, 1 c. c., and the recognition of the several species or 

 kinds of microorganisms present. This process, as carried 

 out, is as follows : 



Place several 1 c. c. pipettes, graduated in 1-10 c. c., 

 in a pipette box and sterilize in the dry heat oven in the 

 usual way. Liquefy 3 gelatin tubes and with a sterilized 

 cooled pipette transfer into tube No. 1 one c.c. of the water ; 

 into tube No. 2 place one-half c.c., and into tube No. 3 one 

 drop of the water. Gently agitate the contents of the 

 tubes, to secure complete mixture, then pour the gelatin 

 onto sterilized glass plates, observing the usual precau- 

 tions in making plate cultures. Set aside the gelatin 

 plates thus obtained for two or three days and then count 

 the colonies when sufficiently developed. 



When only a small number of colonies are present 

 the counting can be done with the unaided eye, but when, 

 as it frequently happens, the number is very large, it is 

 desirable to make use of a counting apparatus that of 

 Wolffhiigel is usually employed. The gelatin plate on 

 which the colonies are to be counted is placed on the 

 black glass base and covered with a glass plate ruled into 

 squares. The number of colonies under six or more 

 squares is thus easily determined, and in this way the 



