

THE PRINCIPLE OF VITAL AFFINITY. 307 
of carbon and hydrogen. The composition of most fats is stated by Liebig to be 
Cw» Hy O,; and we have thus, therefore, another compound formed apparently by 
vital affinity, indicating a peculiar attraction of the two first elements for one an- 
other, and a feeble attraction for oxygen. Indeed, in the composition of wax 
(one of this family of compounds), as stated by MuLDER, the proportion of oxygen 
is only one equivalent to 24 of carbon; in cholesterine, the proportion of carbon 
to oxygen is stated as high as 36 to 1; and in many volatile oils, no oxygen has 
been detected. 
Supposing such a peculiar affinity to act, there is obviously no difficulty (on look- 
ing at the numbers indicating the proportions of the elements) in understanding the 
formation of these compounds out of starch (Cy Hi, O,), just as there is none 
in understanding the formation of starch or sugar (although by an affinity occur- 
ring only in living bodies, and which we regard as vital) from carbonic acid and 
water (CO, + HO), in living vegetables, where a continual evolution of oxygen 
attends the growth; particularly if we suppose that the carbonic acid taken in 
by the leaves and roots, is carried to, and decomposed in, all parts of the plant : 
the formation of the fatty compounds, is, no doubt, one of the processes by which 
the oxygen is set free. But in the case of animals, where (with the exception of 
some of the infusory tribes) there is no evolution of oxygen, the formation of 
fat from starch presents a difficulty. Yet the numerous observations and expe- 
riments of Lirpic and of CHEVREUL and MILNE-EDWaRDs, leave no room for 
doubt that various animals, fed chiefly on varieties of starch, or bees fed on sugar, 
form a much larger quantity of fat, oil, or wax, than they have received mixed 
with their food, and this when they are exhaling no pure oxygen, but, on the 
contrary, compounds of hydrogen and carbon with oxygen, viz., water and carbonic 
acid. Indeed, Dr Ropert THomson having ascertained by repeated experi- 
ments, that the quantity of butter yielded by cows bears no fixed proportion to 
the quantity of oleaginous matter contained in their food, varying indeed from 
one quarter to nearly the whole of the oleaginous ingesta, thinks himself justified 
in inferring that “the butter cannot be supplied from the oil of the food.” (On 
the Food of Animals, p. 156.) 
It is quite certain that in this action, in all animal bodies, the greater part of 
the oxygen of the starch employed must unite with a portion of its carbon and 
hydrogen, and pass off in the excretions just noticed, leaving the small remainder 
of the oxygen in combination with the predominant quantities of carbon and hy- 
drogen. 
It appears possible, indeed, that a// the oxygen which must be separated 
from starch before it can be converted into fat, may be evolved in combination 
with part of the carbon and hydrogen of the starch, without any constituent of 
the air taking any part in the process; but the quantity of fat formed would 
then be small, and it is also possible that the oxygen of the air may be concerned 
