III.

These chances and these causes of general mortality depend upon the atmospheric influences, the mephitism of the soil, the density of the population, and the excellence of the food and shelter, as well as upon the natural vigor and strength of the individual.

Some classes of human beings have greater tenacity of life than others, but all are affected by vicious influences, and yield sooner or later to the elements of destruction. "Everything in the animal economy is regulated by fixed and positive laws."

"We live on our forces," says Galen: "as long as our forces are sound, we can resist everything; when they become weak, a trifle injures us." The truth of this remark is well illustrated in the life of the soldier, whose health is in exact ratio to the condition in which he is placed. And his mode of existence, the combined influence of food, exposure, and the training of mind and body, give a peculiar character, which requires, when disabled, special modification of treatment, and a particular kind of experience. The ancient physiologists distinguished two kinds, or rather two provisions of strength--the forces in reserve and the forces in use; or, as they said, "Vires in posse et vires in actu;" or, as Barthez describes it, the radical forces and the acting forces.

The young soldier, supported by this buoyancy of the unknown force of life, recovers from terrible shocks and disasters to his system, while the old man, fatigued and exhausted by the great and protracted labors of

## active campaigns, feels that he has the hidden resources--the reserved and

superabundant powers of youth--no longer.