bad conductor. In hot climates also we find the hair thick on the backs of animals, and the negro's head woolly, because hair is a non-conductor; and here it serves to protect from the heat of the external world. The top of the head in man occupies the same position, as the uppermost surface of the body, as the back does in quadrupeds. Now, if the protective qualities of the hair are rendered unnecessary by extraneous aids, the hair, having no longer a use, will tend to fall off.
It has always been noticed that scholars and those who work their brains hard, lose their hair very early, and I believe the cause of this is that, having a constant over-supply of blood to the brain (for, as we know, the greatest quantity of blood goes to the organ most in use), the head becomes over-hot, and the hair falls off, in order to provide a sort of natural safety-valve by which the surplus of heat may be got rid of. The close covering of the head with hats and caps is also a prevalent cause of baldness. Such baldness is a common characteristic of the Turks and the Spanish Jews, for among these peoples the head covering is never removed, and is only changed at night. This perpetual covering, carried on from the earliest infancy, when a well-wadded cap is tied under the baby's chin, retards the growth of the hair, and hastens its fall; and the transmitted tendency becomes an hereditary cause of baldness.
It is noticeable that in England baldness is most common among the upper middle classes. The
