THE METABOLISM OF THE BODY. 457 



gestion ; but often there seems to be a general break — the whole 

 metabolism of the body seems to be out of gear ; and the same 

 applies to our domestic animals. If we assume a constant 

 nervous influence over the metabolic processes, this is compre- 

 hensible. The centers can produce only so much of what we 

 may call nervous force, using the term in the sense of directive 

 power; and if this be unduly diverted to the muscles, other 

 parts must suffer. 



On this view also the value of rest or change of work 

 becomes clear. The nervous centers are not without some re- 

 semblance to a battery ; at most, the latter can generate only a 

 definite quantity of electricity, and, if a portion of this be di- 

 verted along one conductor, less must rentein to pass by any 

 other. 



It is of practical importance to recognize that under great 

 excitement unusual discharges from a nerve-center may lead 

 to unwonted functional activity; thus, under the stimulus of 

 the occasion an animal may in a race originate musculajr con- 

 tractions that he could not call forth under other circumstances. 

 Such are always dangerous. We might speak of a reserve or 

 residual nerve force, the expenditure of which results in serious 

 disability. 



It seems that the usually taught 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 appear to be 

 warranted in making a wider generalization. To regard pro- 

 cesses concerned in building up a tissue as apart from those that 

 are recognized as constituting its function, seems with the knowl- 

 edge we at present possess, to be illogical and unwise. Whether, 

 in the course of evolution, certain nerves, or, as seems more 

 likely, certain nerve-flbers in the body of nerve-trunks, have 

 become the medium of impulses that are restricted to regulat- 

 ing certain phases of m.etabolism — as e. g., expulsion of formed 

 products in gland-cells — is not, from a general point of view, 

 improbable, and is a fitting subject for further investigation. 

 But it will be seen that we should regard all nerves as " tro- 

 phic " in the wider sense. What is most needed, apparently, is 

 a more just estimation of the relative parts played by blood 

 and blood- pressure, and the direct influence of the nervous 

 system on the life-work of the cell. 



