212 ELEMENTS OF WATER BACTERIOLOGY 



is present. " The cream is torn or altogether dissociated 

 by the development of gas, so that the surface of the 

 medium is covered with stringy, pinkish-white masses 

 of coagulated casein, enclosing a number of gas-bubbles. 

 The main portion of the tube formerly occupied by the 

 milk now contains a colorless, thin, watery whey, with a 

 few casein lumps adhering here and there to the sides 

 of the tube. When the tube is opened, the whey has a 

 smell of butyric acid and is acid in reaction. Under 

 the microscope the whey is found to contain numerous 

 rods, some motile, others motionless." 



Since this organism is not present in very large num- 

 bers, even in sewage, the test of a water-supply must 

 be made with large samples, and the concentration 

 of at least 2000 c.c. of water by filtration through a 

 Pasteur filter is recommended by Horrocks as a necessary 

 prelude (Horrocks, 1901). The Committee on Standard 

 Methods of Water Analysis (191 2) recommends the 

 following enrichment procedure for the isolation of B. 

 sporogenes which avoids physical concentration. Vari- 

 ous dilutions of the water to be tested are incubated 

 in fermentation tubes containing liver broth for 24 hours 

 at 37°. If B. sporogenes is present gas will be evolved 

 and a characteristic " vile odor " will be produced. 

 If this reaction is obtained the contents of each posi- 

 tive tube is transferred to an Erlenmeyer flask or large 

 test-tube and heated at 80° C. for 10 minutes to destroy 

 vegetative cells. One c.c. of broth containing sediment 

 is withdrawn from the bottom of each flask and enriched 

 once more in a fresh liver broth tube. B. sporogenes 

 will now usually be present in pure culture showing 



