CHAMQES OF OX FAT INTO HUMAN FAT. 596 



2°. The purposes served by the fat. — In all healthy animals which 

 »ake a sufficient quantity of exercise to maintain tliem in a healthy con- 



Cirhon. Water. 



Starch, consisting; of 12 + 10, represented by Ci2 Hio Oio 



Caiie sugar, consistini; of 12 + lli represented by Cia Ilu Oil 

 Paf, again, margarine for example, the solid fat of the humiu body, is represented (p. 

 559, note,) by Cj7 HiO O5 Compare this with 4 of starch, and we have— 

 4 of starch = C4S II40 Oio 



1 of margarine = Ci? H35 O5. 



Difference = Cii H4 O33 



This dUTorence is equal to, or may be represented by, 



U of carbonic acid + 4 of water + 9 of oxygen 



11 coi +4110 + 90 



So that by the separation of carbonic acid, which may be given off from the lunga — of 

 water, which may or may not remain in the system, — and of a portion of oxygen, which 

 may be used up in various ways in the blood, the starch or sugar of the food may be con- 

 verted into fat. 



That in some such way these substances may be changed into the fat of animals was first 

 insisted upon and explained by L^ebig ; and it is probable, as I have said in the text, that in 

 case-i of emergency fat is really formed in the animal body from such kinds of food. But 

 when Liebig put forth his views on this subject, it was not known that vegetable substances 

 naturally contained so large a proportion of fat as has since been found in them. The ne- 

 cessity for the constant production or formation of fat in the body itself, therefore, is not now 

 eo apparent, and the soundest opinion, according to our present knowledge, seems to be 

 that, while the vegetable food usuaily supplies all the fat ready formed which the animal re- 

 quires, yet that a conversion of a certain part of the starch, ^um, sugar, and even of the cel- 

 lular fibre of the food, into fat, may take place, when all the wants of the body are not sup- 

 plied by the fat which the food naturally contains. Of course this opinion applies only to 

 animals in perfect health. In certain diseased states of the body a larger and more con- 

 stant production of fat from the food may Lnke place, as appears to be the case in animals 

 which no diminution of food seems to prevent from kyinif on fat. 



2^. IIoiD the peculiar kinda of fat in the body tnay be difrivedfrom the peculiar kinds of fat 

 in the food. 



a. We have already seen (p. 55S)that the solid part of butler, of olive oil, and of the goose, 

 is identical with the so.'id fat of the human body. When eaten by man, therefore, these se- 

 veral kinds of fat may be at once conveyed, without change, from the stomach to the several 

 parts of the body whei-e they are required. From this circumstanoe these kinds of fat seem 

 remarkably fitted for tlie foo i of man. 



b. The solid fat of the ox and the sheep is called stoarine. TIpon this man hves much 

 and converts it into the solid fat (margarine) of his own body. This may take place after 

 the following maimer :— 



2 of margarine = C?! II72 Oio 



1 of stearine = C74 Hg9 O7 



Diff3rence = Ca H3 O3 



If we double this difference, we have Cg Hi Os ; which is the formula for lactic acid. 

 Recent researches, however, have failed in detecting this acid in the blood — if it be formed 

 at all, therefore, it must exist only in a transition state, and mu.st be sneeiiily converted into 

 other compounds. The final result may pos.sibly be the evolution of the 3 of carbon (Us ) 

 by tlie lungs in the form of carbonic acid. 



c. That the body or its parts pos-<es:i the power of easily transforming these different kinds 

 of fat one into the other, we know, also, from other facta. Thus the calf lives upon milk, 

 and from the two kinds of fat contained in the crea-in of the milk, it forms the solid and liquid 

 fats of its own body. The stearine of the animal in this case may be formed from the mar- 

 garine of the butter, hein-i exactly the converse of the previous case, while the butter oil may 

 be changed into the Uquid fat of the tallow. 



This latter is more difficult »o explain, since the composition of elainc — the liquid fat of 

 the ox, calf, and .sheep— compared with that of butter oil, presents a considerable difference. 

 Thus— 



Elaine = €47 \Ui Os 



Butter oil = C37 IIo3 Os 



Diff.jrence . . . , z=Cio II9 

 What becomes of thi.«t difference, Cio 119, we are unable as yet precisely to explain. By 

 tlie intervention of a little oxygen it misht readily give rise to a little more fat. 



d. The cow and ciilf to.'^ethcr, however, illustrate very clearly tlie existence of this trans- 

 forming power of the animal body. We are unacquiinted, as yet. with the composition of 

 the several kinds of fat which occur in vegetables — but we know that out of these the cow 

 can form the two kinils of fat — the stearine and the elaitie — which exist in its own tallow, 

 and at the same time the two kirejs of fat — margarine and butter-oil — which are found in ita 

 milk. The calf, again, can change these two latter fats into these which ita own body, as 



