490 ANAEROBIC BACTERIA 



it for twelve to eighteen hours. 1 The rabbit will be found to be enor- 

 mously distended with gas. The tissues, particularly the muscles, 

 will be found to be soft, partly liquefied, and the course of the blood- 

 vessels will be marked out by rows of gas bubbles. The organisms are 

 found in greatest abundance in the liver, which is light colored 2 and 

 in typical cases so thoroughly fermented that it appears to be a collec- 

 tion of gas bubbles. The gas bubbles found in the blood stream and 

 in the muscles and particularly in the liver are the result of the 

 decomposition of the muscle sugar and glycogen by this organism. 



FIG. 67. Bacillus aerogenes capsulatus, capsule stain. X 1000. 



Growth on Artificial Media. Anaerobic growth on gelatin is variable ; 

 some strains do not grow in this medium, others produce a slight 

 liquefaction. In plain broth there is a slight turbidity; in broth con- 

 taining dextrose or lactose the turbidity is marked. The reaction in 

 milk has been described previously, the characteristic features being 

 a stormy fermentation, a slight pink color to the undissolved casein, 

 and gas bubbles together with a slight odor of butyric acid. If the 

 milk has not been heated sufficiently to remove all oxygen the organism 

 frequently produces coagulation, but no stormy fermentation and no 

 gas. 



Conditions of Growth. The organism is an obligate anaerobe which 

 does not grow below 20 C., or above 45 C. The optimum tempera- 

 ture of growth is 37.5 C. The spores are quite resistant; five minutes' 

 boiling usually fails to kill them. They are extremely resistant to 



1 This procedure is frequently known as the "Welch Nuttall Test." 



2 The absence of darkening of the liver tissue indicates that little or no proteolysis 

 is taking place; otherwise the liver would be discolored, due to the production of sul- 

 phide of iron from the liberation of H2& of protein and its reaction upon the blood. 



