150 BUTYRIC ACID FERMENTATION 



ledge on the subject (and one well worthy of perusal) shows how very divergent 

 are the substances which now bear the name of " cellulose." He separated a 

 number of these, and collected them into the group of hemicelluloses, distinguished 

 by their solubility in hot dilute mineral acids, whereby they are converted into 

 glucose, whilst the remaining celluloses do not undergo this change. Considering 

 how divergent these substances are, it is not surprising that different investigators 

 do not always obtain concordant results as regards the products of cellulose 

 fermentation. This decomposition occurs on a large scale in the mud of marshes 

 where there is no lack of decaying plants, and where, moreover, the other 

 conditions are favourable. It has long been known to chemists that, in such 

 water, a somewhat copious discharge of gas bubbles rises out of the ground, 

 which discharge consists for the most part of methane (CH 4 ), i.e. the gas to 

 which the name of marsh-gas has been given, from the places where it is found 

 in Nature. Carbon dioxide is also liberated at the same time. The proportional 

 quantity of the two products was reported in several analyses communicated by 

 POPOFF (I.) in 1875, and more accurate researches on the same point were 

 published by HOPPE-SEYLER (I.) in 1886. The latter kept, with exclusion of 

 air, either mud from marshes and rivers, or else clean paper inoculated with a 

 little mud and then distributed in water, and demonstrated that in the mixture 

 of gases evolved therefrom methane predominated greatly at the outset, but 

 thereafter gradually diminished to the proportion i : i, so that Hoppe-Seyler, 

 being unable to discover any other decomposition products, expressed the 

 opinion that the cellulose is hydrolised by the action of the bacteria which from 

 microscopic examination he asserted to be the same as Van Tieghem's Bacillus 

 amylobacter and is then split up into equal volumes of methane and carbon 

 dioxide, according to the equations 



C 6 H 10 O e + H 2 ^ C 6 H 12 6 . 

 C 6 H 12 6 = 3C0 2 + sCH 4 . 



He found the ratio different when sulphates (gypsum, &c.) or ferric salts 

 were present in the water or mud. In such case the nascent methane, by its 

 reducing action on these salts, converts them into carbonates, sulphuretted 

 hydrogen being liberated, according to the equation 



CaSO + CH 4 = CaC0 3 + H 2 S + H 2 0. 



The sulphuretted hydrogen is, then, under natural conditions, acted upon by 

 the sulphur bacteria which are always present in such waters. This will be 

 dealt with in chapter xxxv. 



The importance of cellulose fermentation in the physiology of nutrition 

 (especially of cattle) must also be briefly adverted to. The opinion long held by 

 Emil Wolff, that the vegetable fibres consumed with the food pass out of the 

 alimentary canal unaltered, was contradicted, in the case of ruminants, as far 

 back as 1854, by Haubner, who showed that even in the case of sawdust and 

 paper pulp mixed with the fodder, only a portion (less than half) was expelled 

 again in the excrement, a fact confirmed by the exhaustive researches of Henne- 

 berg and Stohmann. The difference between the amounts of cellulose (crude 

 fibre) taken in and rejected was highest in the case of ruminants (up to 75 per 

 cent.), being only 50 per cent, at most in horses, and still less in the human 

 subject and in swine. In carnivora (dogs), on the other hand, no such difference 

 could be detected. The quantities of cellulose thus disappearing in digestion 

 were, it was thought, digested, and were regarded as approximately equivalent 

 in nutritive value to the soluble carbohydrates. A number of animal physio- 

 logists maintained that the cellulose was dissolved by an intestinal enzyme, 

 which, however, was sought for in vain. The earliest reliable determinations 



