Birds and All Nature, Vol. 5, No. 3, March 1899 / Illustrated by Color Photography

by Various

The coloring of most fish so that they cannot readily be seen by looking down into the water because of the blackness of their backs, is highly protective. And the fact is more apparent when we note that an enemy looking at the same fish from below is hindered in discovery because the white under parts of the fish are hard to distinguish against the light of the sky above. Nearly all the protective color markings of animals are modifications of the scarf skin.

The true skin is of great interest both because it is the seat of what is called the sense of touch and because it is used so extensively in the arts in the form of leather.

Nerves of sensation expand over the whole surface of the body, and their minute branchings in the skin make contact with other substances highly discernible. But the sense of touch is peculiarly developed in few of the lower animals, and we may almost regard it as an attribute of man alone. Our ability to turn our fingers about things and move our hands over their surface gives us a power that is rare in nature. We can tell whether things are hot or cold, rough or smooth, sharp or blunt, wet or dry, and gather many other items of interest which the other senses are incapable of compassing.

A monkey can wind his tail about a nut and tell by the sense of touch whether it is worth his while to crack it. The elephant moves the tips of his trunk carefully over the surface of what he wishes to examine and gets knowledge he can depend upon. But it is the hand of man that shows the highest order of development of touch. By it blind men know their friends and read their books, bank clerks detect the qualities of the notes they handle, and a thousand deft acts in the arts are accomplished.

The true skin is covered with minute projections called papillæ. They may be traced in the palm by the ridges of the scarf skin. They are arranged there in rows so that while the naked eye does not discern the projections individually the rows of them may be noticed on the surface of the scarf skin. Some of these papillæ contain blood vessels and others corpuscles of touch. Some papillæ are small and simple, others compound. In one square inch of the palm have been counted 8,100 compound and 20,000 smaller papillæ arranged in regular rows. There seem to be different end organs for different sensations. There are different spots which may be touched with a fine pointed pencil of copper which is quite hot and no feeling will result. Perhaps the same identical spots touched by the same point, after having been immersed in ice water, will give sensations of cold. Hot spots and cold spots may be found and marked upon the skin. There are more hot spots than cold ones. Either of these when disturbed electrically will give sensations of heat or cold when neither heat nor cold is applied.

Ashe mentions an experiment which shows that the body is not equipped exactly alike on both sides, for when both hands are placed in hot water the heat seems greater to the left than to the right hand. Aristotle wrote of the peculiar feeling produced by placing the ends of the first and second fingers upon a small substance like a pea. With the fingers in their natural position you feel one small round body. Place the same fingers upon the same pea, but with one finger crossed over the other so as to touch the pea on the other side, and you distinctly feel two peas. Another of the freaks of touch may easily be tried by placing the palms together so that fingers and thumbs are against their fellows. Close the hands partly and open them again repeatedly and in a short time instead of each finger's feeling another finger there will seem to be an oiled pane of glass between the hands keeping the fingers about a quarter of an inch apart. The delusion subsides when you look at your hands.

Leather was very early known in Egypt and Greece, and the thongs of manufactured hides were used by all nations for ropes, harness, and other instruments. The renowned Gordian knot, 330 B. C., was of leather thongs. A leather cannon was made in Edinburgh at the time of the American revolution. Although it was fired three times and found to answer, and other firearms were made of this material, it never became common. Had it not been for Mother Goose the leather gun might have dropped from the memory of man.

Leather is made from the true skin and tannic acid. The processes of tanning have recently undergone such changes and improvements that it is out of the question to follow them briefly. The union of the white fibres of gelatin, gluten, and kindred substances with the tannic acid, forms insoluble compounds which have great resistance and strength. This acid is found in oak and hemlock bark, and also in that of many other trees such as willow, ash, larch, sumac, and terra japonica. Tea is one-fourth tannic acid.

Deer skin makes the finer kinds of morocco, while sheep and goat skin make the grades that are used in book-binding. Seal skin makes a superior kind of enamelled leather for boots, bags, dressing-cases, and ornamental articles. Hog skin is so full of oil that it resists the tannic acid, yet saddles are made from it, and it has other uses. The French glove makers produce a very good kid glove from rat skin which can be distinguished from the real article only with a microscope.

The tanner applies the term, skin, to the smaller product taken from calves, dogs, rats, cats, and small game, reserving the dignified name of hide for that of the full-grown ox or horse, while the skin from a two-year-old steer is called a kip.