538 THE PHYSIOLOGY OF ALIMENTATION. 



It is needful to know the general composition of the aliment, and to 

 distinguish between substances which merit the name and those which 

 usurp it, in order to understand its function. We must follow its 

 various transformations, and fix the quantity of the ration of repose as 

 compared with that of the person when working actively. We must 

 determine the effects of inanition, of insufficient nourishment, and of 

 superabundant nourishment. In a word, we must examine the most 

 intimate and delicate reactions by which the organism exhausts itself 

 and repairs its wastes; and, to repeat the expression of a celebrated 

 physiologist we must inspect "the kitchen of vital phenomena." 

 Neither Apicius, nor Brillat Savarin, nor Berchoux, nor the moralists, 

 nor the economists can serve as our guides. It will be necessary to 

 consult those scientists who, following the example of Lavoisier, Ber- 

 zelius, Regnault, and Liebig, have applied the resources of general 

 science to the study of life and thus have founded the chemistry of 

 biology. 



This branch of physiology has made very considerable progress 

 within the last half century, and now maintains separately its methods, 

 its technique, its chairs in universities, its laboratories, and its collec- 

 tions. Its special application is to the study of the "material changes" 

 or metabolism of living beings. Two branches of this subject have 

 been studied: First, the composition of the materials going to make 

 up the organism has been determined, and second, qualitative and 

 quantitative analyses have been made of all the substances entering 

 or leaving it. This includes all that is absorbed through respiratory 

 and food channels on the one hand, and all excreta through the various 

 channels on the other. Thus the nutritive balance sheet has been made 

 out corresponding to various conditions of life both naturally and arti- 

 ficially reared. It can be said which items go to sustain and benefit, 

 which to exhaust and reduce, and which finally strike the balance. 



We do not propose to give a detailed account of this scientific move- 

 ment, for that is a field for special treatises. We intend merely to 

 indicate here the most important results of these laborious researches, 

 including the general laws which have been built up and the theories 

 which have been sustained. This is as far as the subject belongs to 

 general science, and is of interest to the nonspecial reader. Matters 

 of detail have no lack of historians ; it is far more profitable to show 

 the trend of ideas. The theories of alimentation present many concep- 

 tions of the operation of vital functions. There is so great a number 

 of conflicting opinions on this subject that it is not without interest to 

 attempt to clear it up. 



I. 



CI. Bernard remarked, in respect to life, that it is impossible to give 

 it a scientific definition. And this is true not only of life, but of nutri- 

 tion and in particular of the aliment. All the physiologists and phy- 



