CONDITIONS WHICH INFLUENCE NUTK1T1ON. 389 



iological exercise, consumes, so to speak, a definite amount 

 of the limited life of the part. Physiological exercise 

 increases disassimilation, but it also increases the activity of 

 nutrition and favors development. It is a favorite sophism 

 to assert that bodily or mental effort is made always at the 

 expense of a definite amount of vitality and matter consumed. 

 This is partly true, but mainly false. Work involves change 

 into effete matter ; but when restricted within physiological 

 limits, it engenders a corresponding activity of nutrition, 

 assuming, of course, that the supply from without be suffi- 

 cient, Other things being equal, a man will live longer 

 under a system of physiological exercise of every part, than 

 if he made the least effort possible. It is, indeed, only by 

 such use of parts that they can undergo proper development 

 and become the seat of normal nutrition. But notwith- 

 standing all these facts, life is self-limited. Unless subjected 

 to some process which arrests all changes, such as cold, the 

 action of preservative fluids, etc., organic substances are con- 

 stantly undergoing transformation. In the living body, their 

 disassimilation and nutrition are unceasing ; and after they 

 are removed from the influence of what is called life, they 

 change, first losing irritability, or becoming incapable of 

 performing their functions, and afterward decomposing into 

 matters which, like the results of their disassimilation, are 

 destined to be appropriated by the vegetable kingdom. 

 Nutrition sufficient to supply the physiological decay of 

 parts cannot continue indefinitely. The wonderful forces 

 in the fecundated ovum lead it through a process of develop- 

 ment that requires, in the human subject, more than twenty 

 years for its completion ; and when development ceases, no 

 one can say why it becomes arrested, nor can we give any 

 sufficient reason why, with a sufficient and appropriate sup- 

 ply of material, a man should not grow indefinitely. After 

 the being is fully developed, and during what is known as 

 the adult period, the supply seems to be about equal to the 

 waste. But after this, nutrition gradually becomes deficient, 



