BACTERIOLOGICAL STUDY OF WATER. 447 



naturally present in water, particularly the pathogenic 

 varieties. 



NOTE. In determining if the organisms found are 

 possessed of pathogenic properties, in what way will 

 your tests be influenced by this observation ? 



From recent investigations upon this subject it ap- 

 pears that the difference in behavior toward heat of 

 bacteria present in water may have a very important 

 application. Dr. Theobald Smith has recently suggested 

 a method by which it is easily possible to isolate, from 

 waters in which they are present, certain organisms that 

 are of the utmost importance in influencing our judg- 

 ment upon the fitness of the water for domestic use. 

 By the addition of small quantities, one, two, or three 

 drops of the suspicious water to fermentation tubes (see 

 article on Fermentation Tube) containing bouillon to 

 which 2 per cent, of glucose has been added, and keep- 

 ing them at the temperature of the body, 37 to 38 

 C., the growth of the intestinal bacteria that may be 

 present in the water is favored, while that of the water 

 organisms is not ; in consequence, after from thirty-six 

 to forty-eight hours the fermentation, characteristic of 

 most of these organisms, is evidenced by the accumula- 

 tion of gas in the closed end of the tube. From these 

 tubes the growing bacteria can then be easily isolated 

 by the plate method, and it will not be infrequent to 

 find intestinal bacteria present in pure culture. 



Another method for the same object is to collect a 

 sample of about 100 c.c. of the water to be tested in a 

 sterilized flask, and add to this about 25 c.c. of steril- 

 ized bouillon of four times the usual strength. This 



