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Influence of Nervoas System on Cell life. 301 
explain the whole round of facts. Take another instance of 
the influence over metabolism of the nervous system. 
Every athlete knows that he may overstrain, 7. e., he may 
use his muscles so much as to disturb the balance of his 
powers somewhere, very frequently his digestion, but often 
there seems to be a general break—the whole metabolism 
of the body seems to be out of gear. If we assume a con- 
stant nervous influence over the metabolic processes, this is 
comprehensible. The centres can produce so much only of 
what we may cail nervous force, using the term in the sense 
of directive power, and if this be unduly diverted to the 
muscles, other parts must suffer. The same holds of exces- 
sive mental application. 
On this view, also, the value of rest or change of occupa- 
tion becomes clear. The nervous centres are not without 
some resemblance to a battery; at most the latter can gen- 
erate only a definite quantity of electricity, and if a portion 
of this be diverted along one conductor, less must remain to 
pass by any other. 
It is of practical importance to recognize that, under 
great excitement, unusual discharges from a nerve centre 
may lead to unwonted functional activity ; thus, under the 
stimulus of the occasion, a man may in a boat-race originate 
muscular contractions he could not by the strongest efforts 
of his will cause under other circumstances. Such are 
always dangerous. We might speak ofa reserve or residual 
nerve force, the expenditure of which results in serious dis- 
ability. It also applies tomental and emotional effects, as 
well as muscular, and seems to us to throw light upon many 
of the failures and successes (so-called) of life. 
It seems that our past views of secretion and nutrition 
have been partial rather than erroneous in themselves, and 
it is a question whether it would not be well to substitute 
some other terms for them, or, at least, to recognize them 
more clearly as phases of a universal metabolism. We ap- 
pear to be warranted in making a wider generalization. 
To regard processes concerned in building up a tissue, as 
apart from those that are recognized as constituting ite 
