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THE POPULAR SCIENCE MONTHLY.

their severity as far as possible. When Nature crushes him, she is unconscious of it, unconscious of herself: man, so small, is greater than these blind greatnesses, because his peculiar greatness is consciousness. The subject we have been studying is a grand proof of this; but its full, imposing interest would not be understood were we to end without giving the answer to the last question it suggests. Whence comes this heat developed by chemical phenomena in the living system? It comes from aliments which, in the last resort, are all drawn from plants, and they have borrowed it from the sun. When the vegetables, whose combustion takes place within the animal, there throw off a certain amount of potential energy, as heat, they do but transmit to it the force which the sun has supplied them with. It is, then, a portion of solar radiation, stored up at first by the plant, which the animal makes disposable and converts to use, whether for resisting cold or for securing the regular play of his motive functions. Thus we may say, with exact truth, the sun is the inexhaustible source, as it is the perpetual spring of life. From this point of view, science confirms the intuitions of oldest date, and man's poetic dreams in the childhood of the race. Reason completes the instructions of its long experience by harmonious agreement with the simple and natural sentiment felt by the first of men, when for the first time they looked on the splendor of day.—Revue des Deux Mondes.

 

NERVOUS HEALTH AND MORAL HEALTH.

AN able article in the Times some weeks ago on "Brain-work and Longevity," which has since been discussed and rediscussed in all sections of the press, was remarkable for several characteristics, especially for a curious thesis apparently indorsed by the Lancet of a subsequent week, that overwork of the brain, through late hours and the like, is a physiological impossibility. The argument was something of this kind: All brain-work means the destruction of nervous tissue or brain-tissue; all such tissue, when destroyed, must be repaired by food and sleep before it can be drawn upon again; therefore, overwork is impossible. A man may try to steal hours from sleep; but, if he does, he will only find how hopeless the attempt is the moment he passes the bounds of what the existing amount of tissue permits. He will struggle feebly against sleep, drop asleep, find he is doing no good, and be compelled, in the interests of his work, to shorten the hours of his work. The argument is full of fallacies, as any one might tell who applied a parallel argument to prove the impossibility of overwalking; and we are astonished at the sort of sanction given to it by the Lancet. It is quite as easy to prove that no man can overwalk himself. He cannot walk except by the destruction of muscular tissue, and, when as