Nutrition. 223 



have been made. The composition of everything passing 

 into the body and the exact composition of everything 

 passing out of it is a tedious experiment to make, and one 

 liable to considerable error. 



Boussingault many years ago made income and expendi- 

 ture experiments on all domesticated animals, and recently 

 a most elaborate balance-sheet has been drawn up for the 

 horse from the experiments of Zuntz and Lehmann* I 

 have reproduced this table, converting the weights into 

 pounds and ounces ; this latter has occasioned a slight 

 discrepancy, inasmuch as the elements expended do not 

 agree exactly with those taken in. The error, however, is 

 trivial, and the table is introduced as an example of how 

 observations of this kind are made. The first portion of it 

 illustrates also the method by which digestion experiments 

 are carried out. As the horse on which this experiment was 

 carried out neither lost nor gained weight, and was kept at 

 rest, it is evident that the income balanced the expenditure, 

 so that the quantities representing the income are the 

 amounts of the elements required by this horse for 24 

 hours. 



In looking at income and expenditure tables of a 

 body in perfect equilibrium, it is necessary to remember 

 that, though the amount of the elements going out corre- 

 spond to the amount taken in, the elements passing away 

 are not immediately derived from those which have passed 

 in ; everything passing out must have been of tissue origin, 

 and have formed part and parcel of the tissues. To make 

 the matter clearer, take the nitrogen in the table — viz., 

 nearly 3 ozs. per diem — excreted by the kidneys : it does 

 not follow that this nitrogen was derived from the 18 ozs. 

 of proteid entering the system, but it was derived from 

 18 ozs. of living proteid which formed part of the 

 body. 



* ' Landwirthschaftliche Jahrbucher,' Band xviii., 1889, Heft 1. 



