594 
THE FOOD WE GIVE. 
and of horse-fat and train-oil in certain oily seeds. In these 
the fat must arise^, just as in animals, by the same cliemical 
process of an imperfect transformation. The most favor¬ 
able conditions to the development of tallow are food destitute 
of nitrogen, w’armth, and want of exercise. Warmth is per¬ 
fectly indispensable to the production of tallow in an animal. 
Tallow is so easily consumed by the oxygen of the air that it 
is employed to produce animal heat, if there be any deficiency 
in this. Martel (Trmis, Lmn. Soc., \o\. x\, p. 411) mentions 
the case of a fat pig which was overwhelmed in a slip of earth, 
and lived for l60 days without food, and was found to have 
diminished in weight during that time 120 lbs. Its fat had 
been consumed in supporting respiration, just as that of 
hybernating animals during winter. Motion also diminishes 
the tendency of an animal to fatten, by increasing the number 
of its respirations, and, therefore, by giving to the system an 
increased supply of oxygen gas, which consumes the tallow. 
Hence our practice of stall-feeding cattle. A few considera¬ 
tions will show that it is quite impossible to draw up any 
series of numbers to represent the equiyalent values of the 
food; for we must first know the object for which the food is 
intended. In a cold day the animals ought to be furnished 
with food containing a considerable amount of unazotized 
ingredients, in order to protect them from the effects of the 
cold. The equivalent values of potatoes and beans could not 
be compared, because their respective value as food arises 
from totally different causes. Potatoes are of great use in 
keeping up the heat of the body and in forming tallow, but 
are in the highest degree unprofitable for forming flesh; 
1550 lbs. of potatoes would be required to form the same 
quantity of Jlesh that 100lbs. of beans would do; whilst little 
more than 200 lbs. would suffice to form the same quantity 
of tallow; hence the great advantage of mixing food so as 
to supply in smaller bulk those constituents of which one 
kind of food is deficient. Sheep fed on oilcake increase in 
weight faster than on any other kind of food; but they feel 
quite soft, and when fat handle like a bag of oil. * I'his is 
because they receive food which contains very little albumen 
to form flesh, so that tallow is the only product. But if with 
the oilcake they receive oats or barley, they are firm to the 
touch, and possess plenty of good flesh, and the fat lies 
equally distributed amongst the muscular fibre. The reason 
here also is obvious, for both oats and barley contain much 
albumen. 
As I have elsewhere remarked, that vegetable substances 
contained animal matters ready formed, was a sus[)icion 
