To a general in the battlefield, human life is a factor which, if properly used, can destroy the enemy. To an engineer human life is an equivalent to energy, or a capacity to do work, mental or muscular, and the moment something is found to be a source of energy and to have the capacity of doing work, the first thing to do, from the engineer’s point of view, is to analyse the generator with a view to discovering how best to conserve it, to improve it, and bring it to the level of maximum productivity. Human beings are very complicated energy-producing batteries differing widely in quality and magnitude of productive power. Experience has shown that these batteries are, first of all, chemical batteries producing a mysterious energy. If these batteries are not supplied periodically with a more or less constant quantity of some chemical elements called food and air, the batteries will cease to function—they will die. In the examination of the structure of these batteries we find that the chemical base is very much accentuated all through the structure. This chemical generator is divided into branches each of which has a very different rôle which it must perform in harmony with all the others. The mechanical parts of the structure are built in conformity to the rules of mechanics and are automatically furnished with lubrication and with chemical supplies for automatically renewing worn-out parts. The chemical processes not only deposit particles of mass for the structure of the generator but produce some very powerful unknown kinds of energies or vibrations which make all the chemical parts function; we find also a mysterious apparatus with a complex of wires which we call brain glands, and nerves; and, finally, these human batteries have the remarkable capacity of reproduction.