
FOODS, IN RELATION TO RESPIRATION AND FEEDING. 337 
be thus accounted for. It is worthy of observation, however, that in this 
series the amounts of the nitrogenous constituents consumed are in an inverse 
ratio to those of the non-nitrogenous ; and if we are to calculate, that in the 
ease of a defect of the latter or an excess of the former, a notable portion of 
the nitrogenous constituents would serve as respiratory material, such an 
assumption in the present case would tend yet more clearly to show the closer 
dependence of consumption upon respiration, than upon the supplies by the 
food of-the plastic elements of nutrition, as such. 
In the next and last series of experiments to be noticed with sheep, as far 
as possible the same description of foods is used throughout; but animals 
of different breeds and weights and other admitted qualities are now the 
subject of experiment in the several pens. The breeds which have thus been 
compared are,—the Hampshire Down, Sussex Down, Cotswold, Leicester, 
Half-bred Wethers (Leicester and Southdown), and Half-bred Ewes 
(Leicester and Southdown). In all these experiments oil-cake and clover- 
chaff were the limited foods, and Swedish turnips the complementary food. 
About 1 Ib. per head per day of each of the limited foods was given to the 
Hampshires ; and taking this allowance as the standard, the other breeds had 
quantities of these foods exactly in proportion to their weights. There were 
from 40 to 50 sheep in each lot; and each experiment extended over several 
months. The experiments were, however, not all made in the same season ; 
the turnips were therefore of different growths ; and the oil-cake and clover- 
chaff, though chosen as nearly as possible of similar quality, were not always 
from the same stocks. These circumstances, then, as well as the intrinsic 
differences in the breeds themselves, if any, might be supposed perhaps to 
have some share in any variations in result. We see, however, that there 
is nevertheless a very striking coincidence in the amounts of constituents 
consumed to a given weight of animal among the different breeds. But. 
what is more to the purpose, the amounts of non-nitrogenous substance 
consumed to a given weight of animal by these different breeds, and at 
different times, are, after making, as before, due allowance for the probable 
different equivalents of the foods, exactly consistent with the indications of 
the other series with all their varied foods. This result, then, further shows that 
in all, the respiratory and fat-forming exigences of the animals have fixed 
the limit to their consumption of food; and also that these requirements have, 
on an average, and under somewhat similar circumstances, a pretty constant 
relationship to their weights. With this general coincidence in the amount 
of non-nitrogenous substance consumed to a given weight of animal in the 
several pens of this series, there could not, of course, with foods of similar 
composition in all, be much variation in the amounts of the nitrogenous con- 
stituents taken under the same circumstances. Of these, however, we have 
throughout this series twice or thrice as much as in many cases of the other 
series, which would not happen if the demand for them had been the guide 
to consumption ; nor shall we afterwards find that the increase in weight 
obtained was by any means proportional to this large amount of nitrogenous 
substance consumed. 
In our experiments with sheep, then, whether with different descriptions 
of food, or with different breeds of the animal, the amount of food consumed 
would seem to be regulated by the quantities which it supplied of the non-nitro- 
genous rather than by those of the nitrogenous constituents. 
So much, then, for the bearing of our sheep experiments upon the question 
‘of the amount of food consumed according to its composition: but before 
entering upon a consideration of the results of these same experiments in 
relation to the second question, namely, that of the increase produced, it 
1852. ‘ Z 
