4 i 6 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 com- 

 bustion 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 com- 

 pletes 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 strug- 

 gle 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 ap- 

 plied 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 can- 

 not walk except by the destruction of muscular tissue, and, when as 



