The skin is a protective covering often referred to as a garment: a most incomplete metaphor. It is such a one as no Parisian modiste or Bond Street tailor ever devised. It adjusts itself to all seasons. In the winter by various clever schemes it saves the body all the heat possible, while in summer it has ways of radiating heat. Its texture varies in thickness as necessity arises. It actually covers the eyeballs but is of extreme thinness here, thus offering little obstruction to the passage of light.
At areas subjected to great chafing and wear there is corresponding thickness. The tough soles of barefooted people and the horny-handed manual laborer are familiar to all. Sad experience has taught the danger of blisters when soft skin comes in contact with heavy tools. When the chafing reaches a point where the tough outer layer can no longer afford enough protection to the delicate inner layers, nature comes to the rescue with what the medical men call a bulla, but what we run-of-the-mill people are all too familiar with as a blister. As you know, the live tissues are always saturated with a thin fluid. This collects between the outer and inner layers, and although we do not like it, nevertheless it affords much protection to the tender tissues beneath. But if the skin is allowed to accustom itself slowly, the responsive thickening is certain.
Dr. Francesco Ronchese, of Providence, Rhode Island, has a most interesting little book with many illustrations, called Occupational Marks. Habitual pressure of a tool will produce a heavy callus at a typical position. The modern increasing use of mechanical gadgets must modify these marks. Still the professional boxer, particularly if he is a “ham,” will probably show cauliflower ears. The granite cutter for years has used power-driven chisels and will continue to have a ring of callus around his little finger.
Soon after 1890 Mark Twain wrote his book about Pudd’nhead Wilson, the story of a lawyer in a Mississippi town who became interested in the whorls and marks in the skin of the finger tips. A mulatto woman changed her son with the white child of the family where she worked. Pudd’nhead finger-printed the children in infancy and when the grown-up pseudo-heir committed murder years later, he was identified by his finger markings.
Evidently Mark Twain learned early of the work that led later to the almost universal finger-printing in modern communities. These markings are friction ridges found principally on the finger tips where we do so much grasping and they help to prevent slipping. Once again our pride is humbled as we learn that certain monkeys have such friction ridges in their prehensile tails. These ridges extend into the depths of the skin, or rather vice versa. When Jimmy Valentine sandpapered the tips of his fingers to get more delicate feeling, the ridges soon grew back in the same underlying pattern.
Dr. Ronchese points out that in rare cases the typical markings may be absent, owing to leprosy in the tropics, radiation by X-ray or radium, and even skin grafting. Then occupational marks might well be a help in identification.
The nails are really not a great deal different from the hard outer layer of the skin, being formed in much the same way. The tips of the fingers are tremendously important to us and they are very sensitive and exposed to injury. That evidently is the reason why at these places, instead of hard heavy calluses, the dead remnants of the live cells are packed tightly together to form the nails. At the upper end of each nail is a thick collection of live cells just below the surface. This is called the matrix and is the growing part of the nail. As these cells die, they are pushed along the bed of the nail. You are all familiar with the process as you find it necessary to cut or file off the lower end. It is said that nails usually grow at the rate of two inches a year.
If the whole nail is pulled off, a new one can thus be formed in a few months and theoretically it should be just as good as the old one. If any part of the matrix is destroyed, however, the scar of this will always show thereafter in the nail. Any injury to the nail itself, as by nail polish, is a temporary affair; therefore, it is on the whole a harmless if barbaric practice to use modern beauty aids here. Similarly, nail biting is not a serious habit except from the aesthetic point of view.