OF SECRETION IN GENERAL. 



577 



various excretions, in the five cases already referred to ( 566) ; water being 

 excluded in each case : 



Ingested as Food. 



Excreted. 



Total 



43236.7 



2594.0 



1539.1 



39112.6 



The water ingested amounted on an average to about three times the solid 

 matters ; that egested in various ways was commonly between one-fifth and one- 

 sixth more, showing that there is an absolute production of water in the system 

 ( 569). The following table gives the general results of the comparison of the 

 matters assimilated and excreted, so calculated that the sum in each case 

 amounts to 100 : 



620. It is . obvious that the demand for the performance of the Excretory 

 processes generally will, in the first place, arise, as in the case of Respiration, 

 from the continual disintegration and decay to which the organized fabric is 

 liable in the maintenance of a merely vegetative existence ; and this will be con- 

 stant during the whole life of Man, as of any other warm-blooded animal, its 

 amount varying with the degree of general vital activity. But, secondly, the 

 exercise of the animal functions, involving (as this does) the disintegration of 

 the nervous and muscular tissues as the very condition of the evolution of their 

 respective forces, becomes a special source of the production of excrementitious 

 matter, the amount of which will vary with that of the forces thus developed. 

 The removal of excrementitious matter may become necessary, thirdly, from the 

 decomposition of superfluous aliment, which has never been assimilated. This 

 would not be the case, if the amount of food prepared by the digestive process, 

 and taken up by absorption into the current of the circulation, were always 

 strictly proportional to the demand for nutriment created by the wants of the 

 system ; but such a limitation seldom exists practically, in those individuals at 

 least who do not feel themselves obliged to put a restraint upon the indulgence 

 of their ordinary appetite ; and all that is not appropriated to the reparation of 

 the waste, or to the increase of the bulk of the body, must be thrown off by the 

 excretory organs. It has been already shown that an abundance of nutritive 

 material in the blood does not augment the production of the ordinary tissues 

 to any considerable extent ( 596) ; and it would appear that all such materials 

 as are not speedily assimilated pass rapidly into a state of retrograde meta- 

 morphosis. How large a proportion of the solid matters of the urine ordina- 

 rily has this source, will appear from facts hereafter to be stated ( 640). More- 

 over, in the last place, it cannot be deemed improbable that the changes which 

 the crude aliment undergoes, from the time of its first reception into the absorb- 

 ents and bloodvessels, to that of its conversion into organized tissues and special 

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