418 FATTY ELEMENTS OF FOOD, AND ON FATTENING. 



the economy, as it were. Such observations have naturally led 

 physiologists to conclude that the fatty principles of the food were 

 the principal, if not the only sources whence animals derive the fat 

 which is met with stored up in their tissues, or which appears in the 

 butter of their milk. And this view, so long as the carnivorous 

 tribes alone are considered, has not a single feature which makes it 

 objectionable. But when we would extend it to the herbivorous 

 tribes, two difficulties meet us on the threshold of the inquiry. 



1st. Do vegetables actually contain such a quantity of fatty matter 

 in their structure as will explain the fattening of cattle and the for- 

 mation of milk 1 



2d. Is it not more simple to suppose fat and butter the product of 

 certain transformations undergone by starch and sugar in the animal 

 economy 1 



It appears at first sight most opposite to nature to suppose that the 

 feeding ox finds the whole of the fat he lays on ready formed in the 

 food he eats ; it is only, in fact, after having made repeated analyses 

 of plants, and discovered fatty matters almost everywhere, and in 

 quantities generally superior to any that had been suspected in the 

 composition of plants, that the idea begins to acquire likelihood ; 

 finally, the chemist becomes convinced that it is so when he finds a 

 regular association of neutral azotized substances and fatty principles 

 in all the articles usually employed as food for cattle, — in the grass- 

 es and cereals, in the leaves and stems and seeds of plants. 



Fatty substances appear to be principally formed in the leaves, 

 where they frequently show themselves under the form and with 

 the properties of wax. Taken into the bodies of animals, mingled 

 with the blood, and exposed to the influence of the oxygen of the 

 inspired air, they will undergo an incipient oxidation, whence will 

 result the stearic or oleic acid that is found as a constituent of suet. 

 By undergoing a second elaboration in the bodies of the carnivora, 

 the same fatty substances, oxidated anew, would produce the mar- 

 garic acid which characterizes their fat. These divers principles, 

 by a still further degree of oxidation, would give rise to the fat vola- 

 tile acids which make their appearance in the blood and in the per- 

 spiration. Finally, did they suffer complete oxidation, i. e. combus- 

 tion, they would be changed into carbonic acid and water, and be in 

 this shape eliminated from the economy. 



Among the various properties possessed by fatty substances, there 

 is one which may play an important part in the phenomena of fatten- 

 ing ; this is the solvent power which they severally possess in re- 

 gard to one another ; the property of mixing in all imaginable pro- 

 portions, still preserving the general features which severally dis- 

 tinguish them. In the stomach, in the intestines, in the chyle, and 

 in the blood, fatty substances of various kinds may form homoge- 

 neous matters by their intimate admixture, and become divided into 

 globules of complex composition, but everywhere the same. 



Another property of fatty matters of every kind, which deserves 

 particular attention, is that of insolubility in water. We find, in 

 fact, that when an animal eats a soluble substance, that in general il 



