Being the most delicate, the cells of the central nervous system usually die first, and we then say that the man is dead. So the body may be, but much of the protoplasm of which it is composed—whole organs, in fact—remains alive; the muscles will respond to electrical stimulation, and in case some people may dispute that this is a sign of life, if pieces of his skin be removed and grafted into another person, they will grow there, produce hair, and become, in fact, a part of the new body. This they could not possibly do if they were dead; we cannot endow inanimate matter with life. As death creeps on over the tissues, the leucocytes die, and in doing so form a ferment which solidifies one of the proteids dissolved in the blood, so that the familiar clotting takes place. By a similar process certain constituents of the muscles are also clotted, the muscles stiffening and passing into what is technically, but also pretty generally, known as rigor mortis. Rigor is said to set in soon after death if the body is kept in a warm place, or if death has been preceded by violent exercise; but death in this instance means only the death of the body. It is at the precise moment that a muscle fibre dies that it passes into rigor. By keeping it cool, so that the processes of life may go on slowly, especially if it be in a healthy condition, its death may be deferred for hours; while, on the other hand, at the end of a severe and protracted battle, exhausted soldiers sometimes die instantaneously on being shot, and are found fixed in the position in which the fatal bullet found them—on their knees, with gun to shoulder, in the act of firing. But if the manner of death is not to be lightly dealt with, its causes are still more obscure. It seems natural enough that people should be killed by violence or by diseases with an external or septic origin, or even by one particular organ wearing out and involving the whole body in the fate of its part. But why should people die of old age? Why should their vitality ebb till they quietly go out? Life is a mechanical cycle of changes. For a time even after it has stopped growing, the body replaces what it wastes, and keeps itself in a condition of equilibrium. Why, then, without any apparent external cause, does it, after a more or less circumscribed period, enter into a decline? And, finally, could we, by taking the proper precautions, delay or prevent old age and death? In the first place, regarding protoplasm as a chemical structure, why, if kept under favourable conditions, should it ever break down? We have no reason to suppose that it need. It is hard to see how the minute animals, consisting of only one cell, can die of old age, provided that no injurious influence be brought to bear upon them. When an individual has grown to a certain size, it divides in two, and each enters upon life afresh. Why, therefore, should not all the cells of the body continue to renew their youth?