Hair is an outgrowth from the cells of the skin, just as certain skin cells form into the sweat glands and oily or sebaceous glands, or into fingernails or toenails. Just as certain cells of the mucous membrane of the mouth form into teeth so do certain cells in the skin evolve into hairs.
If we were to watch this process by making microscopic sections of the skin of an unborn child, we would find that at a certain stage some cells of the skin begin to grow downward in a solid column. From below certain other cells grow up to meet this columncells which later become connective tissue around the hair root. A small loop of blood vessel begins to push itself upward, and finally penetrates into a sort of bay at the bottom of the hair root.
It is this blood vessel which will nourish the hair-making cells. From the side of the root there grows out a set of cells which produce an oily secretion thrown right on the hair as it grows upward. The central part of this hair root begins to form itself into the hair itself, which grows upward through the skin in the form of dead chiton-like cells.
If now we follow this hair along through its entire life, we find that it frequently breaks off close to the root and a new hair begins to form.
This pushes the old dead hair out and grows in in its place. When we have understood this we understand a great deal about the treatment of hair trouble.
The hair itself has no canal in it, no sap. Hairs get their sustenance from the blood. It, therefore, cannot be nourished or encouraged to grow by external applications, like a plant. When baldness occurs it is due to the withdrawing of the blood supply and the consequent atrophy of the hair root.