It appears from this and a number of other experiments that glucoses and dextrin are formed by the cerealin, the former only being decomposed by the bacteria almost as fast as it is produced, for after three hours no glucose is found in the drenches.
We have thus shown that the acids and gases are produced from the starch contained in the bran, the starch being first changed into glucoses by the action of an unorganised ferment or ferments; and that the glucoses are decomposed by a specific organism, the nitrogenous material in the bran serving for its nutriment; that the action is the same with or without skins although there appears to be a little more H2S gas given off from drenches containing skins, than from those containing none.
The ferment has no direct action on the skins. This may be shown by taking a piece of limed skin, in which a considerable portion of the lime exists as carbonate, and submitting it to the action of the ferment; in this case the action goes on much longer than in the drenches, being complete in about 15 days, but the skin may be left in the resulting liquid for three months without undergoing further change than solution of the lime, provided that suitable means be taken to exclude moulds, which, by destroying the organic salts and acids produced, enable putrefactive fermentation to begin.
It has been thought that the bran itself exercised some peculiar action on the skin, and possibly this may be so to a slight extent,[172] as the sweet bran drench is occasionally used on the continent, but if skins are placed in a mixture of bran and water (in the proportions for drenching) which is prevented from working by the addition of a minute quantity of HgCl2 1/10000, such a drench has no action on them, and when tanned they are harsh and hard, similar experiments have been made on a smaller scale, using ether and chloroform to prevent fermentation, with the same results.
In order to show whether the acids alone were the cause of the action on the skins, an artificial drench was made up of the following composition—
0·5 grm. per 1000 glacial acetic acid.
1·0 " " " lactic acid sp. gr. 1·210.
In this skins were worked intermittently for 1 1/2 –2 hours, and it was found that in this time they were in a similar condition to skins which had been in a drench from 12–16 hours. They were afterwards tanned, and found to be good leather, and in every way equal to similar skins which had been “drenched.” A number of experiments have been tried with sulphuric and hydrochloric acids in order to ascertain if these had a similar action, but the results have not been satisfactory.
With regard to the third portion of the research, viz. the products of a pure cultivation of the bacteria, we have obtained a good number of results; but as the description of the experiments is of a greater length than we anticipated, and as there is still some work to do in verifying them, we are obliged to leave this portion for another paper, which we hope to have ready by the next session.
In conclusion, we may summarise the results obtained up to the present in the fermentation of bran by the organism we have used; remarking that there may be other organisms capable of fermenting bran in a somewhat similar manner.