578 ON SOME OF THE ANIMALS FED AND SLADGHTEEED AS HOLAN FOOD. 
certain, that independently of the mere mpply of constituents, the conditions of concen- 
tratim, and MgestibiUty, and consequently of msimilahhty of oiu- different food,, mm,, 
have their share in determining the relative values for the vai-ymg eagencies ot the 
system, of substances which, in a more general, or more purely 
justly be looked upon as mutually replaceable. It would, indeed, hardly be supposed 
that substances so distinct, both morphologically and chemically, as fuf ^ 
under all circumstances, be equally adapted to the conditions supplied within the li in^ 
organism, and be so at an equal cost to its energies even though they may eac even- 
tually subsei-ve the Fat-storing and respiratory requirements of the bo y. 
It is then, fully granted, that in the study of this branch of Physiological Chemistry, 
as in that of others, the facts peculiar to Physiology herself must be allowed an important 
place • though, it is at the same time claimed, that those of Clwmstry be not excluo ^ 
By the aid of ChemiMry it may be established-that, in the admmture of Anmaf food 
with Bread, the relation, in estimated respiratory and fat-forming capacity, o t ie /loa- 
nitrogenous to the Nitrogenous substance, will be increased ; and further— that, in sue., 
a mixed diet, the proportion of the non-nitrogenous constituents which wall be m t le 
concentrated condition, so to speak, oifat itself, will be considerably greater than in Biead 
alone. Common experience testifies, moreover, that certain advantages are so eim(. 
It is for Physiology to lend her aid to the full explanation of the facts and cone usion, 
which Chemistry and common usage may in them turn determine. 
