92 BACTERIOLOGY. 



quently, a very common product. Marsh-gas is found 

 wherever cellulose is undergoing- decomposition. It is 

 sometimes an important constituent of the intestinal gases. 

 The volatile amine compounds have been already referred 

 to. Carbon monoxide may possibly occur among the 

 bacterial products. 



Free nitrogen and hydrogen are sometimes met with. 

 Sulphur occurs frequently in the gaseous condition as 

 hydrogen sulphide. Phosphorus may likewise appear as 

 phosphuretted hydrogen. It is evident, therefore, that 

 proteins, as well as carbohydrates, give off gaseous decom- 

 position products. 



The formation of gas bubbles is made use of in differ- 

 entiating one species from another. Thus, the colon 

 bacillus produces gas in abundance, whereas the typhoid 

 bacillus does not. The anaerobic bacteria possess especial- 

 ly marked aerogenic properties. 



As a result of abnormal fermentations in the stomach, 

 or in the intestines, a considerable amount of gas may be 

 produced. Moreover, in certain bacterial diseases, as 

 symptomatic anthrax, a marked accumulation of gas may 

 occur in the subcutaneous tissue. In such cases a distinct 

 crackling sensation is felt when the fingers are passed over 

 the skin. An interesting pathological phenomenon is met 

 with in the so-called "foaming liver." On the cut surface 

 of this organ gas bubbles may appear and form a scum 

 which rapidly increases in thickness. When this foam is 

 removed a new one will form. This peculiar condition is, 

 of course, met with only when certain markedly aerogenic 

 bacteria are present. Inasmuch as the gases produced fre- 

 quently contain marsh-gas and hydrogen they will burn on 

 contact with a lighted match. 



The various bacteria can be designated, or grouped, 

 according to the characteristic action which they induce. 



