
FOODS, IN RELATION TO RESPIRATION AND FEEDING. 351 
pended in the direct production in the animal body of one part of fat. At 
any rate, we are safe in assuming this amount for our present purpose, in the 
absence of more exact knowledge than is at command on the nature of the 
intermediate changes to which the constituents of food are subject in their 
passage through the body. If, then, we suppose, that the starch series—rather 
than the proteine compounds—of the food, served for the formation of the 
fat in the animal body, it follows, that about 25 parts of these were expended 
in the formation of the 10 parts of produced fat. If now we add to this 
amount of the non-nitrogenous constituents of the food not fat, the 34rd parts 
which were fatty matter already formed, and also the 12rds of the increase 
which was not fat, it would appear, that at least $0 parts of the 100 of dry 
substance consumed, must have been directly employed in the production of 
the 15 only of dry animal increase. It is obvious, too, from the nature of the 
chemical change by which fat would be formed from the starch series of 
compounds, that the extra 15 of the 30 parts of the dry substance of the 
food, which were expended in the direct production of the 15 of dry increase, 
would not serve any useful purpose in the respiratory process of the fattening 
animal. And, unless indeed, we were to assume—that in the more direct use 
of the starch series of compounds as respiratory matter, their oxygen was 
eliminated only in combination with respiratory material—and that when em- 
ployed in the production of faé it was not so—it would appear, that not only 
must this produced fat have been obtained at the cost of respiratory material 
expended by the fattening animal which produced it—but that it is, at any 
rate, not in the amount of respiratory material thus obtained, that there can 
be any gain in this conversion by the fattening animal of a given amount of 
compounds of dower respiratory and fat-forming capacity, into fat to serve 
as human food, of which it is the most concentrated of the respiratory con- 
stituents. 
If, then, as we have seen, so large a proportion as nearly 3rd of the dry 
substance of the food of the fattening pig may be employed in the direct 
production of increase—and we have reason to suppose that frequently more 
than this is so employed—we think that the deviations from uniformity in the 
amounts of non-nitrogenous constituents consumed by a given weight of 
animal, within a given time, as shown in our tables, will be admitted to be 
even less than might have been expected in so extensive and varied a series 
of experiments—and to be, by no means such, as to raise any question as to 
whether or not, it was the supplies of the respiratory and fat-forming, rather 
than the flesh-forming constituents of the foods, which determined the 
amounts consumed. 
But to recur to the question of the formation of fat in the animal body. 
We believe that such a formation, even to a considerable, and practically 
important extent, is demonstrated by the results of the experiments with pigs 
last given; and there is every reason to believe, that it is the starch and other 
non-nitrogenous constituents of the food that contribute mainly, if not en- 
tirely, to this formation. 
At one time MM. Dumas and Boussingault maintained that the formation 
of fat in the animal body was improbable; and others have done so more re- 
cently. Since that time, however, both M. Boussingault and M. Persoz have 
instituted direct experiments in reference to this question. In the course of 
these experiments they found a decided formation of fat; and most probably 
from the starch series of compounds. 
M. Boussingault made numerous experiments of a somewhat artificial kind 
with ducks ; from which it appeared, that fat might be formed in the body 
from other non-nitrogenous constituents of food, and probably from nitroge- 
