72 



the animal. The mean percentage of nitrogenous matters in the skin 

 is 26.35, and as the skin consists of almost half its weight of water, it is 

 seen that the dry skin would contain 50 per cent of its weight of nitrog- 

 enous materials. The next most important ingredient is of course the 

 fat, of which the average is 22.89. In the nitrogenous substances the 

 proteids comprise about half of the whole. Of the other half two- thirds 

 belong to the gelatinoids and one third to the flesh bases. The skin, 

 therefore, is preeminently a gelatinous body. About one-half of the 

 total quantity of nitrogenous substances it contains is soluble in hot 

 water, and one-third of the half which is soluble is not precipitated by 

 bromin. If the gelatinous matters of the skin could be easily separated, 

 they would be the most valuable parts of the animal for the prepara- 

 tion of the liesh bases. Skins of animals, however, are usually more 

 valuable for the manufacture of leather than for any other purposes. 



To go a little more into the detail of the data representing the com- 

 position of the skin, we find that the skin which had the largest per- 

 centage of water belonged to the Tamworth pig, and the one with the 

 smallest to the Duroc Jersey, No. 5. Of fat the largest amount was 

 found in the Duroc Jersey, No. 5, thus showing again the general rela- 

 tion of the proportions of water and fat to which attention has already 

 been called. The smallest percentage of fat was found also in the case 

 of the skin of the Tamworth, where the percentage of water was 

 largest. In regard to nitrogenous substances the most remarkable 

 variations are seen. In the Berkshire, which contained the largest 

 proportion of nitrogenous substances, the true proteids comprise by 

 far the larger portion, followed by the gelatinoids, while the flesh bases 

 form a very small percentage of the whole. On the other hand, in the 

 skin of the Duroc Jersey, No. 5 the quantity of proteids is compara- 

 tively small, while both the gelatinoids and flesh bases are high. 

 Whether this marked peculiarity in the composition of the skin is due 

 to the influence of the breed or to accidental causes can not be stated. 

 Probably, however, it is due to accidental causes 5 as, for instance, the 

 Chester White and the Duroc Jersey, No. 5 show similar composition 

 of skins, but this is quite different from the composition of the skin of 

 Duroc Jerseys, Nos. and 7. It is possible, further, that owing to the 

 peculiar structure of the skin and the difficulty of securing a homoge- 

 neous mixture of it, portions of the skin from different cuts vary 

 relatively in the sample which was taken for analysis. Thus, for 

 instance, if a portion of the skin very rich in gelatinous matter and 

 flesh bases should form an excessive portion of the whole sample taken 

 for analysis, the effect would be the same as is seen in the data recorded. 

 The summation of the analyses is generally satisfactory, yet in one 

 case there is a deficit of 9 percent, while in another there is an excess 

 of 1.70 per cent. These variations are doubtless due to the difficulty 

 of securing a homogeneous sample for analytical purposes. Another 

 source of unreliability in the samples of skin is found in the difficulty 



