The Puering, Bating & Drenching of Skins

by Joseph Turney Wood

The enzymes contained in dog dung which are effective in the puering process belong to several groups, principally the proteolytic and lipolytic groups, but indirectly enzymes of the first group (see p. [132]), (fermenting carbohydrates) and of the fifth group (fermenting urea) also play some part by decomposing various compounds (e.g. cellulose and urea) contained in the puer.

The action of certain enzymes from the animal body upon skin has been tried by the author.[103] Those selected were pepsin and pancreatin,[104] as being most likely to be present in dung. Pepsin only acts in presence of HCl. Two portions of the same skin were taken, one of them was treated with a 1 per cent. solution of pepsin, acidified with 0·2 per cent. of hydrochloric acid; the other in a bate liquor of dogs’ dung (puer), both at a temperature of 40°C. At the end of one hour the skin in the pepsin solution was considerably “fallen,” but that in the manure solution was bated nearly away, i.e. the greater part of it was dissolved. A 1 per cent. solution of pancreatin (Mercks) was found to act far more rapidly than pepsin; 1·5 per cent. of chloroform was added to the solution, to prevent the development of bacteria. The skin was reduced, but had not the peculiar touch of a puered skin. As will be shown later, this was found to be due to the absence of any chemical action upon the lime salts in the skin, and consequently it felt “limey.” This action took place in the puered skin, but not in the skin treated with pancreatin alone.

W. J. Salomon ([19]) has also attributed the activity of the bate to pepsin and pancreatin, but he does not give any proof of the presence of these ferments in the bate.

Since it is practically impossible up to the present, to separate these enzymes from the dung in a state of purity, the method described on p. [134] was employed.

The enzymes prepared in this way consist of a mixture of all the enzymes present in the dung, the amount obtained from 1000 grm. of dung being about 4 grm. The product had a slight diastatic action upon starch; 0·5 grm. in 100 c.c. of water at 35° C. was found to have a very considerable reducing action upon skin, and when combined with the amine compounds prepared from the dung, the action was more powerful, and more rapid than with puer. Limed skin was puered in thirty minutes in this solution to a perfect condition, in the absence of bacteria, and with no evil smelling compounds. The reaction of the solution at the beginning of the experiment was faintly alkaline; at the end of the experiment it was considerably alkaline.

This experiment proves that the action of the dung is a complex one, due to the combined action of enzymes and chemical compounds upon the skin. These compounds, which are principally amines, and salts of amino-acids, probably assist the enzymes, and at the same time act upon the lime remaining in the skin from the previous liming process. Whether a skin, which has never been submitted to the liming operation, could be bated by enzymes alone, without the addition of amines, has not, so far as I know, been tried, but it is highly probable that this would be the case.

In order to compare the action of the enzymes prepared from dung with that of the enzymes produced by bacteria, a mixed culture of bacteria from puer in dextrose gelatin, after seven days’ growth, was taken. 200 c.c. of this was mixed with 200 c.c. of dilute alcohol (65 per cent.), 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 vacuo. The enzymes thus obtained were re-dissolved in water, and the former experiment with the skin repeated with this solution, with the addition of the amines. The skin was brought down in exactly the same way as before, showing conclusively that it is the enzymes produced by bacteria, acting in conjunction with the amines, which bate the skin. It would seem that the 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 interdependent, i.e. bacterial action alone is insufficient, and chemical action alone is insufficient, the true bating action being a combination of the two.

There seems little doubt that it is the enzymes which dissolve the skin substance, or rather certain parts of the intercellular substance of the fibres, and the compound of this substance with lime. The action is a digestive one, and may be compared, as we have shown, to that of the digestive ferment of the pancreas.