VITAL PI/l-:.\<>Mi:\A OF BACTl. .,'/.! 



101 



FIG. 64 



portion, supported upon a glass base, as shown in Fig. 64. The 

 tube is filled with a culture media consisting of 1 per cent, glucose, 

 peptone bouillon (without air bubbles), and sterilized in the steam 

 sterilizer. It is then inoculated with a loopful of a cul- 

 ture of the organism in question, and observations taken : 



1. If there is a turbidity produced in the open bulb 

 it indicates the presence of an aerobic species; if this 

 clouding occurs only in the closed arm, while the open 

 bull) remains clear, it is an anaerobic species. 



2. The quantity of gas produced daily should be 

 marked on the upright arm; if the tube is graduated a 

 note of it is taken and the percentage calculated on the 

 fourth to the sixth day after gas production has ceased. 



3. A rough analysis of the gas produced may he 

 made as follows: Having signified by a mark on the 

 tube the quantity of gas produced, the open bulb is 

 completely filled with a 10 per cent, solution of soda, 

 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, removing the thumb, the volume of gas left 

 after the union of the NaOH with the CO 2 is noted. The remainder 

 is nitrogen, hydrogen, and marsh-gas. If it is desired to test for the 

 presence of hydrogen, the thumb is again placed over the open end 

 and the gas collected under it. As the thumb is moved a lighted match 

 is brought in contact with the gas. If hydrogen is present a slight 

 explosion occurs. 



Formation of Acids from Alcohol and Other Organic Acids. It has long 

 been known that the bacterium aceti and other allied bacteria convert 

 dilute solutions of ethyl-alcohol, under the influence of oxidation, into 

 acetic acid: 



Fermentation 

 tube. 



CH 3 

 CH 2 OH 



2 



CH 3 

 COOH. 



H 2 0. 



The higher alcohols glycerin, dulcit, mannite, etc. are also con- 

 verted into acids glycerin, indeed, as commonly as sugar. 



Finally, 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 produced. Among the gases formed were chiefly CO 2 and H. 



Thus Pasteur found that anaerobic bacteria convert lactate of lime 

 into butyric acid. 



