It was a rather strange idea of a recent distinguished writer upon Hygiene, that perhaps, if we understood perfectly all the laws of health, and obeyed them all, life might be indefinitely prolonged. Nature around us pronounces otherwise. Every tree, though it live a thousand years, withers, root and branch, at last. All the animals, from the long-lived elephant and tortoise down to the ephemeral insect floating on the breeze, have set terms of life. On this globe of ours, whatever organism is born, dies. Man's body furnishes no exception; his spirit, only, is immortal.

The marvel is, that so delicate a mechanism as the human body can survive for a single year, amongst the various perils that surround it. Yet we live on, some of us, accidents apart, for a good while. Most persons fail to reach advanced age, because of disease. What is disease ?

It is something either being or acting wrong in the body. There may be as many kinds of disorder, or disease, at least, as there are organs of the body. More than that there really are, however; because complications of diseases occur, and each organ, or the general system, may be out of sorts in a large number of different ways.

First, it will be well for us to consider what makes the body, or parts of it, get out of order.