528 THE ANAEROBIC BACTERIA 
of gas bubbles, and the liver will be light colored^ and filled with gas 
blisters. The adrenals are usually deeply congested, and the odor of 
butyric acid is very distinct. If the abdomen of the distended animal 
is tapped with a trocar, and some of the gas collected by downward 
displacement, it will explode with the typical hydrogen "bark" when 
ignited. The gas bubbles in the muscles, the blood stream and the 
liver are the result of the fermentation of the muscle sugar and glycogen 
by the organism.- These two reactions, stormy fermentation in milk, 
and the Welch-Xuttal rabbit test, are presumptive tests for B. welchii. 
They are not conclusive, but strongly suggestive of the presence of 
the organism in the material under investigation. 
Growth in Cultural Media.— B. welchii is readily cultivated in media 
containing utilizable carbohydrate in the absence of oxygen. It grows 
with difficulty in media containing no carbohydrate, unless a supple- 
mentary enrichment with animal protein is available. The organism 
Fig. 71.— Bacillus welchii from pure milk cuture. X 1000. 
grows with very moderate luxuriance in gelatin. The majority of 
cultures which are active produce a softening of this medium which has 
frequently been mistaken for liquefaction of enzymic origin. While 
it is true that gelatin thus acted upon will not become firm when it 
is cooled to the temperature of the ice-box, the true explanation of the 
process is associated with the ability of the organism to form consider- 
able amounts of amino-acids from the gelatin protein.^ This amino- 
acid formation is materially restricted in corresponding media contain- 
ing utilizable carbohydrate. Cultures in plain broth develop a slight 
turbidity; in carbohydrate broths the turbidity is marked, and a row 
of gas bubbles sin-rounrls the free surface of the medium. The gross 
appearance of milk cultures has been described. The characteristic 
1 The absence of darkening of the liver tissue indicates that little or no proteolysis is 
taking place; otherwise, the organ would be discolored due to the production of sulphide 
of iron, formed from the H2S of the tissues and the iron of the hemoglobin. 
- Cultures are readily obtained from the bloodvessels in any part of the body. 
3 .Jour. Infec. Dig., 1922, 30, 141. 
