UTILIZATION OF THE SKINS OF AQUATIC ANIMALS. 329 



The skins of most luaiuiiuils arc composed of four membranes or 

 parts. The first is the fat-bearing tissue, situated between the flesh 

 and the body of the skin; the second or middle portion, known as 

 the dermis or true skin, is made up of layers of fibers interwoven and 

 intersecting in every direction; the third or outer part is a more or 

 loss horny membrane, which contains the nerves, the smaller blood 

 vessels, and the base of the perspiratory glands; the fourth is a thin, 

 semitransparent cellular tissue, known as the epidermis, in which the 

 hair is rooted. The dermis or true skin forms the leather, and the 

 third laver above noted — the horn-like tissue containing the nerves and 

 perspirator}' glands — forms the "grain" or "bloom" of the leather. 

 The fat-bearing tissue and epidermis, as well as the hair, are removed 

 in the various processes of preparing the skin for tanning. In some 

 leathers — for instance, porpoise — the grain or bloom is also removed. 



Many persons in securing aquatic skins fail to appreciate the impor- 

 tance of care in removing them from the dead animals, and through 

 carelessness make many knife-cuts in the membrane. In the case of 

 furs these cuts are not so very serious, since the membrane can be 

 sewed together and the damage concealed by the fur; but w^hen skins 

 are to be used for leather the cut portions are wholly valueless. 



Under ordinary conditions, as soon as life ceases decomposition of 

 the skin l^egins unless a detergent is applied. Salt is ver\^ generally 

 used for this purpose and is plentifully sprinkled over the skin on its 

 removal from the animal. Although effective, salt is not the least 

 injurious agent that may be used, borax being generally more satis- 

 factory and more easily removed by soaking. 



On account of the great range of raw materials and requirements of 

 the leather trLde, the various processes of leather-making are neces- 

 sarily numerous, differing even for skins of the same variety, accord- 

 ing fo their qualit}^, the season of the j^ear, and many other conditions, 

 the correct understanding of which is the outcome of experience. 

 However, the general principle is so far identical in all classes of 

 leather-making that it ma}" be outlined here. 



The skins and hides usually reach the tanner after remaining in salt 

 a greater or less length of time, depending on the distance from the 

 place of slaughter. The first procedure is to cleanse the skins and to 

 loosen and remove the hair and epidermis, neither of which is desired 

 in the finished leather. In case the skins are received direct from the 

 animals, the}'" are easily cleansed from blood and dirt by soaking a few 

 hours in fresh water and then washing for a few minutes in a per- 

 forated rotating drum, known as a wash-wheel, through which a stream 

 of water is constantly flowing. If the skins have been salted, as is 

 usually the case with aquatic pelts, a more thorough soaking and wash- 

 ing, with several changes of water, is necessary, the soaking sometimes 

 extending over several days. In case of large hides which have been 

 heavily salted the process may be assisted ])y a "hide-mill," in which, 



