426 BACTERIOLOGY. 



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, of "Washington, has 

 recently suggested a method by which it is easily pos- 

 sible to isolate, from waters in which they are present, 

 certain organisms that are of the utmost importance in 

 influencing our judgment 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 fer- 

 mentation tubes (see article on Fermentation Tube) 

 containing bouillon to which 2 per cent, of glucose has 

 been added, and keeping thei^ 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 fermenta- 

 tion, characteristic of most of these organisms, is evi- 

 denced by the accumulation 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 

 is then placed in the incubator at 37° to 38° C, for 

 thirty-six to forty-eight hours, after which plates are 



