VITAL ACTIVITIES OF BACTERIA 155 



total quantity, of gas produced, the open bulb is completely 

 filled with a 10% solution of NaOH, the mouth tightly closed 

 with the thumb, and the mixture thoroughly shaken. After 

 a minute or two all the gas is allowed to rise to the top of the 

 closed arm by inclining and turning the tube, and then, re- 

 moving the thumb, the volume of gas left after the union of 

 the NaOH with the CO 2 is noted. The remainder is for the 

 greater part nitrogen, hydrogen, and marsh-gas. If it is de- 

 sired to test for the presence of hydrogen, the open end of the 

 tube is again filled with water, the thumb is again placed 

 over the opening and the gas collected under it. As the 

 thumb is removed a lighted match or gas flame is brought into 

 contact with the gas. If hydrogen is present a slight explo- 

 sion occurs. Hill has devised a tube for collecting the gas in 

 the top of the closed arm by having a ground glass stopper 

 substituted for the sealed end. 



Numerous results have been obtained from the conversion 

 of the fatty acids and their salts into other fatty acids by 

 bacteria. As a rule, the lime salts of lactic, malic, tartaric, 

 and citric acids have been employed, these being converted 

 into various acids by the action of bacteria, such as butyric, 

 proprionic, valerianic, and acetic acids; also succinic acid, 

 ethyl-alcohol, and more rarely, formic acid have been pro- 

 duced. The gases formed were chiefly CO 2 and H. Thus 

 Pasteur found that certain anaerobic bacteria convert lactate 

 of lime into butyric acid. 



