206 
Oh the Hieoretical and Practical Value of 
<loes not possess the power inherent in plants of transforming 
saline, or other, compounds containing nitrogen, into flesh- 
forming matters. Thus it has been shown that animals fed 
exclusively upon starch, sugar, fat, and other food entirely desti- 
tute of albuminous compounds, rapidly lose flesh, and die at the 
end of the fifth or sixth week, or but little later than they would 
have died if no food at all had been given. 
Recent experiments, moreover, have established the fact that 
albuminoids, like starch and other non-nitrogenous compounds, 
are capable of becoming oxidised in the animal system and 
furnishing animal heat ; and it has likewise been shown that the 
albuminous compounds of food, in addition to their power of 
forming muscle, have the property of becoming split up into 
fat and urea during the process of digestion. Indeed, some 
physiologists maintain that the fat of animals is mainly, if not 
entirely, derived from this source, and not from starch or sugar, 
or analogous non-nitrogenous constituents of food. Recent 
physiological experiments with reference to the formation of fat 
from albuminoids, however, are not quite decisive ; and they 
certainly do not invalidate the well-established experience that 
a large proportion, at all events, of the fat of animals is derived 
either from ready-made fatty substances, or from starch and 
other readily assimilable non-nitrogenous compounds in food 
such as is given to fattening oxen, sheep, and pigs. 
Whichever view may be entertained with regard to the fat- 
producing power of albuminoids, they are certainly a most 
important class of compounds ; and it may be laid down as a 
fact, established alike by practice and science, that the nutritive 
value of food depends in a great measure upon a certain amount 
of albuminous compounds, which may be more or less, according 
to the description of the animal, or the purpose for which it 
is kept on the farm. 
2. The non-nitrogenous, or fat- and heat-producing substances, 
may be conveniently divided into three groups : — 
. a. Ready-made fat. 
b. Carbon-hydrates. 
c. Woody-fibre, or cellulose. 
Ready-made fats and oil are by far the most valuable of all 
food-constituents in an economical point of view, for oil or fatty 
matters fetch a higher price than any nitrogenous compounds, 
or than starch, sugar, or any other non-nitrogenous substance. 
Oil and ready-made fatty matters are particularly well adapted to 
the laying on of fat in animals, inasmuch as the composition of 
vegetable fats is analogous to that of the several kinds of fat 
which form part of the bodies of animals. The fatty matters of 
