VITAL PHENOMENA OF BACTERIA. 83 



clouding occurs only in the closed arm, while the open 

 bulb 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 be 

 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 mix- 

 ture 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 new volume of gas formed is permitted to 

 escape. That which passes off is carbonic acid gas; 

 the remainder is nitrogen, hydrogen, and marsh-gas. 



For the quantitative determination of these gases 

 Hein pel's gas pipettes may be used. The principle of 

 the method is this : The hydrogen, mixed with oxygen 

 and passed over red-hot palladium asbestos, becomes 

 water, and thus disappears; the carburetted hydrogen 

 is converted into carbon-dioxide and is estimated as 

 such; the remainder is nitrogen. 



Formation of Acids from Alcohol and Other Organic Acids. 

 It has long been known that the bacterium acetiand other 

 allied bacteria convert dilute solutions of ethyl-alcohol, 

 under the influence of oxidation, into acetic acid: 

 CH 3 + 2 + CH 3 + H 2 0. 



CH 2 OH COOH. 



The higher alcohols glycerin, dulcit, mannit, etc. 

 are also converted into acids glycerin, indeed, as 

 commonly as sugar. 



