194 Theobald Smith 



tion of the oxygen admitted to the confined space, by the 

 vital activity of the bacteria. Again in glucose bouillon in- 

 oculated with hog cholera bacilli, the complete paralysis of 

 the bacteria after a certain stage in the fermentation is very 

 clearly demonstrated by a permanent return of the color of 

 the fluid in the bulb. The contrast between the deep blue 

 color in the latter and the yellowish hue of the decolorized 

 fluid of the closed branch is very striking. 



THE PRODUCTION OF GAS BY BACTERIA. 



Attention has been called to the formation of gas by bacteria 

 by a number of writers in the past. Thus Escherich' in 1885 

 demonstrated the fact that B. coli and B. ladis aerogenes, both 

 bacteria of the intestinal tract described by him for the first 

 time, produce gas in solutions of glucose and lactose. In 

 1886, Arloing* called attention to the same subject. The 

 property of gas production had been long associated with the 

 pathogenic bacillus of ' ' black quarter ' ' in cattle {^Rauschbrand, 

 charbon symptomatique) which produces gas in the tissues of 

 the affected part. Similarly the anaerobic bacilli of tetanus 

 and of malignant oedema are known as gas producers. Among 

 these anaerobes the formation of gas was demonstrated by 

 distributing the bacteria in deep layers of liquid agar contain- 

 ing glucose and congealing the agar at once. The formation 

 of numerous gas bubbles throughout the agar and the break- 

 ing up of the jelly by large quantities of gas is described and 

 pictured and is now a common sight in bacteriological labora- 

 tories. A large number of bacteria belonging mainly to the 

 group of facultative anaerobes, are now known as gas 

 producers. Nevertheless the production of gas by bacteria 

 has not thus far been taken as a serious matter by bacteriolo- 

 gists in the diiferentiation and fixation of species and varieties. 

 Many have of late years been in the habit of recording the 

 presence or absence of gas in cultures, but by methods likely 

 to mislead. Since the gas test has proved the only final 

 means ot differentiating two important species, B. coli commu- 

 nis and B. typhosus, much more attention has been paid to 

 this function but the methods have not materially improved. 



