The Puering, Bating & Drenching of Skins

by Joseph Turney Wood

It was now necessary to ascertain the mode of action of the bacteria on the skins.

I have previously shown[122] the action of digestive ferments or enzymes to be notable in the case of pancreatin. A careful study of the behaviour of the digestive enzymes in the animal body shows, however, pretty conclusively, that they are all destroyed before the fæcal matter is discharged,[123] and, therefore, the enzymes in the dung are not from this source.

An attempt was made to filter the dung diluted with water through a Berkefeld filter, and thus obtain a clear filtrate containing all the enzymes and free from bacteria; it was found impossible to filter the liquid in this way.

The method of Claudio Fermi[124] was also tried, but a clear filtrate could not be obtained.

The author has succeeded in obtaining the enzymes best in the following manner:—About 150 c.c. of the above-mentioned “puer” was well mixed with an equal quantity of glycerin and allowed to stand for seven days; it was then capable of being filtered on a filter pump, although very slowly, and yielded a clear filtrate of a deep golden brown colour; the filtrate was poured in a thin stream into a tall vessel containing about 1500 c.c. of 98 per cent. alcohol. A copious flocculent precipitate of the albuminous matters and enzymes was thrown down, the alcohol was filtered off and the precipitate washed on the filter with absolute alcohol, and dried over sulphuric acid. The resulting amorphous body was of light brown colour, and became darker when exposed to the air. The amount obtained from 150 c.c. of dung was 0·55 grm. (3·66 grm. per litre). The body consists of a mixture[125] of all the enzymes existing in the dung along with other albuminous bodies. It has a very slight diastatic action on starch. 0·5 grm. in 100 c.c. of water at 35° C. had a very considerable reducing action on skin. A further experiment with 0·5 grm. of amine hydrochlorides, 0·5 grm. of enzymes and 100 c.c. of water, at 35° C. brought down a piece of limed sheep grain in 30 minutes exactly like puer; the reaction of the solution at the commencement of the experiment was faintly alkaline; at the end of the experiment it was considerably alkaline.

It was noted that the fæcal odour of the glycerin solution disappeared on standing for two or three weeks, and the solution smelt strongly of ethyl butyrate, the enzymes being still present.

These enzymes were prepared from dung, and it now remained to prepare them in the laboratory by the action of bacteria alone. For this purpose 200 c.c. of a mixed culture of dung bacteria in the solution above described, seven days old, was mixed with 200 c.c. of dilute alcohol (alcohol 65, water 100) and well shaken. Gelatin and albuminoid bodies are by this means precipitated. The liquid was filtered and poured into eight times its volume of 98 per cent. alcohol. The precipitate which came down was washed with absolute alcohol and dried in the usual way. The enzymes thus obtained were redissolved in water and the former experiment with skin repeated with this solution. The same effect was produced, showing conclusively that it is the enzymes produced by the bacteria, acting in conjunction with the amines, which bate the skin. It would seem that the special action of the enzymes is aided by the presence of amine compounds, in addition to the chemical action which these latter have upon the skin. The action is shown to be interdependent, i.e., bacterial action alone is insufficient, and chemical action alone is insufficient, the true bating action being a combination of the two.

In conclusion the author has pleasure in acknowledging the valuable assistance of Mr. H. S. Shrewsbury in carrying out some of the experiments.

III. Further Notes on the Action of the Dung Bate.[126]

The present notes are a continuation of those published in 1898. It has been impossible for me to follow up the subject except in a desultory manner, but I think it desirable to put further results, however meagre, before you with the object of throwing more light on the complex process of bating hides and skins.