492 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 has recently sug- 

 gested 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 

 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 fermentation 

 tubes (see article on Fermentation Tube) containing 

 bouillon to which 2 per cent, of glucose has been added, 

 and keeping 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 char- 

 acteristic of most of these organisms is evidenced 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 to 



