EXCRETION OF SUPERFLUOUS AZOTIZED NUTRIMENT. 295 



separate or strain-off, as it were, the products of the decompo- 

 sition of the tissues formed from it, when their term of life 

 had expired ( 161). But it is certain that Man (as well as 

 other animals which have in some degree learned his habits) 

 frequently consumes much more food than is necessary for 

 the supply of his wants ; and a little consideration will show, 

 that the surplus must pass-off by these excretions, without 

 ever forming part of the living fabric. For new muscular 

 tissue is not formed in proportion to the quantity of aliment 

 supplied, but in proportion to the demand created by the 

 exercise of it ( 587); consequently, if more food be taken-in 

 than is necessary to supply that demand, no use can be 

 made of it. We never find that a Man becomes more fleshy 

 by eating a great deal and taking little exercise ; indeed, the 

 very contrary result happens, his flesh giving place to fat. 

 But let him put his muscles to regular and vigorous exercise, 

 and eat as much as his appetite demands, and they will then 

 increase both in strength and bulk. 



348. Hence, if more azotized food be taken-in, than is 

 required to supply the waste of the muscular and other azotized 

 tissues, the surplus must be carried-off by the organs of 

 excretion chiefly, indeed almost entirely, by the Kidneys. 

 By throwing upon them more than their proper duty, they 

 become disordered and unable to perform their functions ; 

 hence the materials which they ought to separate from the 

 blood accumulate in it, and give rise to various diseases of a 

 more or less serious character, which might have been almost 

 certainly prevented by due regulation of the diet. The most 

 common of these diseases among the higher classes are Gout 

 and Gravel ; both of these may be often traced to the same 

 cause, the accumulation in the blood of lithic acid, which 

 results from the decomposition of the superfluous azotized 

 food, and which the kidneys are not able to throw-off in the 

 proper state, that is, dissolved in water. That these diseases 

 are, comparatively speaking, rare among the lower classes, is 

 at once accounted-for by the fact, that they do not take-in 

 any superfluous azotized food; all that they consume being 

 appropriated to the maintenance of their tissues, and the 

 kidneys having only to discharge their proper function of 

 removing from the blood the products of the decomposition 

 of these. 



