VITAL PHENOMENA OF BACTERIA. 83 
clouding occurs only in the closed arm, while the open 
bulb remains clear, it is an anaérobie 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 
Hempel’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, + 0, + CH, + HO. 
| 
CH,OH COOH. 
The higher alcohols—glycerin, dulcit, mannit, etc. 
—are also converted into acids—glycerin, indeed, as 
commonly as sugar. 
