2i8 METABOLISM 



cultivated anaerobiotically in a nutritive solution in which Swedish filter paper 

 forms the source of carbon and an ammonium salt the source of nitrogen, and 

 to which carbonate of lime is added to neutralize the acids which arise. The 

 cellulose becomes at first transparent, then in the course of a few months 

 entirely dissolves and is broken down into acetic acid, butyric acid, traces of 

 other fatty acids, carbon-dioxide, and water. In a definite case, 3-35 g. of 

 cellulose gave rise to 2-240 g. of acetic and butyric acids (in varying proportions), 

 0-972 g. of carbon-dioxide, and 0-014 g. of hydrogen. Obviously the cellulose 

 is first of all split into simpler carbohydrates ; but it is noteworthy that the 

 bacillus has not as yet been made to develop on any other medium than cellulose. 



The cellulose, which is produced annually in enormous quantities by the 

 higher plants, and which once formed is no longer for the most part of any 

 further (metabolic) service to them, is again made available for metabolism, and 

 thus vast quantities of carbon, which otherwise would lie unused, become trans- 

 formed into humus, turf, and coal, once more to be employed in the support of 

 life. The bacillus mentioned is not the only one which acts in this way. It is 

 frequently stated that methane is also formed from cellulose, and the plentiful 

 occurrence of this gas in places where cellulose is undergoing decomposition is 

 evidence in favour of the correctness of this statement. In a word, Omelianski 

 has succeeded in showing that the cause of this methane-fermentation of cellu- 

 lose is a bacillus, which appears to be like that described, but thinner and more 

 delicate. It grows in a culture solution like that in which the bacillus producing 

 hydrogen-fermentation thrives, but it ferments the cellulose into acetic acid, 

 butyric acid, carbon-dioxide and methane. Omelianski, in one experiment 

 found that 2-0065 g. of cellulose gave rise to 0-1372 g. of methane, 0-8678 g. of 

 carbon-dioxide and 1-0223 g- of volatile acids. Thus about 50 per cent, of the 

 fermentation products are volatile acids, and among these there is about nine 

 times as much acetic acid as butyric acid. 



The Bacteria causing hydrogen and methane-fermentation occur frequently 

 in conjunction in nature and it is extremely difficult to separate them. As 

 long as this separation is not effected the products of the fermentation set up 

 by both organisms appear in the culture, sometimes those of the one predomi- 

 nating, sometimes those of the other. We may suppose, therefore, that the 

 contradictory results arrived at in other fermentation experiments are often 

 due to impure cultures, and hence Omelianski' s work is of extreme value from 

 the point of view of technique. [Omelianski, 1904 a.] 



In addition to cellulose, pectins are among the substances which go to the 

 construction of the cell-membrane. They also are not dissolved out by the plant, 

 but remain in the fallen leaves, twigs, &c., and are attacked by definite micro- 

 organisms in the soil or in water. We have to thank Winogradsky (1895) and 

 Behrens (1902) for proof that certain Bacteria, apparently butyric acid Bacteria, 

 carry out ' pectin fermentation ' in nature, though we are not as yet accurately 

 acquainted with the products of fermentation. Many species of Mucor also 

 are able to dissolve pectins. This dissolution of pectin compounds plays a part 

 also in the technique of hemp and flax manufacture (' retting '), since the 

 isolation of the fibres of these plants is possible only after the dissolution of the 

 middle lamella by pectin-fermentation. [Omelianski, 1904 b.] 



On studying the final products of fermentation, e. g. cellulose-fermentation, 

 we find that they are partly fully oxidized products (carbon-dioxide), partly 

 products of extreme reduction (methane, hydrogen), partly intermediate sub- 

 stances (acetic acid, butyric acid, &c.). All the compounds which are incom- 

 pletely oxidized may still be made use of. Although the actual employment of 

 such energy as may be obtained by oxidation of methane or hydrogen is not as 

 yet known, substances like lactic, butyric, and many other organic acids are, on 

 the other hand, used for respiratory or fermentative purposes by numerous micro- 

 organisms. [The most thoroughly studied of these organic acid fermentations 



