We are quite sure to-day that, roughly estimated, each pound of human flesh represents an amount of potential energy equal to about sixteen million foot-pounds, and that all of the life-processes are, in the last analysis, purely physical, and that they follow physical laws. Any exertion, either muscular or nervous, which we make, over and above that supplied by the energy in our assimilated food, will have to be taken from the stock as represented in the tissue,--consequently, continued work means hunger; if continued longer without food, it means exhaustion, and if continued longer without food and rest intervening, it means the deterioration of the tissues. The recent investigations of Matthews upon the manner of nerve action, and the fact that the same is due to substances known as reversible gelatines, as well as to the cause of the negative variation of nerves exposed to exciting stimuli, all show that these most complex of life's processes are as purely physical, in the largest sense, as the most simple ones. The artificial fertilization of sterile eggs by the use of dilute solutions, whose actions might almost be called catalytic, still further emphasizes the fact that life's processes, even in the embryo, are essentially physical. Take, for instance, the sterile egg of the sea-urchin; the two per cent. solution of potassium cyanide; the continued constant temperature for a definite time, and all of the other conditions which enter into the development of this crude protoplasmic mass, are all physical factors, regardless of the fact that the result is a living organism, where we would, according to our old ideas, certainly expect an undeveloped sterile egg, or a potentially dead body. As with this ovum, so with the vegetable protoplasmic mass in the germinal radical of a seed: if its development is once started, it must continue its natural course without interference, upon pain of speedy degeneration upon interruption, and, in this light, both the egg and the grain of seed are places where life can be started (or motion on a larger scale begun) rather than living things before their development began, or while they were lying in their dormant state.