GENUS BACILLUS 319 



uniformly cloudy appearance to the liquid. Ordinarily there 

 is no membrane on the surface. After some days' standing 

 the growth begins to settle, forming a grayish, friable sedi- 

 ment. If the bouillon contains muscle sugar the reaction will 

 be changed to acid, in from 24 to 48 hours, due to the fermen- 

 tation of the agar. Later, however, the liquid will become 

 strongly alkaline, unless there was too much muscle sugar. 

 In acid bouillon the growth is less vigorous. It grows better 

 in a bouillon containing peptone than in a simple beef broth. 

 In peptonized bouillon containing 1 per cent dextrose, gas 

 appears within 24 hours and continues to form for from three 

 to five days. During the first day from one-fourth to one- 

 half of the total quantity is produced. By the end of the 

 second day the gas formation is nearly at an end. The total 

 amount which collects in the closed branch of the fermenta- 

 tion tube is equivalent to about one-half of the capacity of 

 this branch. The gas set free is composed of CO 2 and an 

 explosive gas which consists largely of H. The ratio of CO 2 to 

 H is approximately as 1 to 2. The reaction of the liquid be- 

 comes strongly acid, which condition checks the multiplica- 

 tion of the bacteria. 



Gas is not produced in bouillon containing lactose or 

 saccharose. These sugars are not fermented. Alkaline cul- 

 tures containing them become more strongly alkaline as the 

 growth continues. 



Milk. When the milk is acid in the beginning it gradu- 

 ally becomes alkaline. There is no precipitation or coagula- 

 tion of the casein. After standing for from two to three weeks 

 in an incubator a gradually developing opalescence of the 

 milk can be observed. Later it becomes clear, then light 

 brownish in color. If allowed to stand longer in the incubator 

 the volume of the culture shrinks by evaporation and the 

 opalescent liquid becomes quite thick and dark-colored but not 

 viscid. "When the opalescence appears the milk is strongly 

 alkaline. The process seems to be a form of saponification of 

 the fat globules due to the presence of the alkali produced by 

 the action of the bacteria. 



