METABOLISM OF FAT. 931 
composition normal to the particular species of animal, are laid down 
directly, and that other portions, such as the excess of stearin which 
occurs in mutton fat, become broken down completely, and either directly 
oxidised, or the products of their decomposition again built up to form 
the normal fat. It has indeed been conclusively proved that the fat of 
the food may be to a certain extent laid down unaltered in the body- 
fat. Dog.s which have been starved for a considerable time, so that 
practically the whole of the body-fat has become removed, will, if fed 
upon an excess of mutton fat and sufficient proteid, lay down a body-fat 
of a melting point and composition very similar to mutton-fat. This 
si lows that at least a portion of the fat introduced with the food has 
been, for a time at any rate, laid down directly as body-fat. 1 
It has been further shown that dogs to which there has been 
administered, along with their food, forms of fat which do not ordinarily 
occur in the animal economy, will lay down a certain amount of this 
along with their body-fat. This has been determined for spermaceti, 
linseed oil, and rape oil.' 2 That in pigs the fat of the body may also be 
derived from the fat of the food, was shown in some of the experiments 
by Lawes and Gilbert. 3 
Formation of fats from fatty acids. — The question of the form 
in which fats are absorbed has been already considered in a previous article 
dealing with that subject, and it has there been shown that the fats of the food 
are in large part not absorbed in the form of fat, but in that of fatty acid, 
into which and glycerin they are broken up by the fat-splitting ferment of 
the pancreatic juice ; and that they undergo a subsequent synthesis into fat 
by combination with glycerin in the columnar epithelial cells of the small 
intestine. 
That such synthesis is possible even in the absence of glycerin given with 
the food, is shown by the experiments of I. Munk, who found that when a 
dog was fed upon fatty acids in place of the fats of its ordinary food, just as 
much fat was absorbed into the chyle and was laid down in the body as if 
it had been fed with the complete fat. The columnar epithelial cells become 
filled with fat globules, as after a meal containing actual fats ; and the synthesis 
of fatty acid and glycerin to form fat must therefore have occurred in these 
cells, which must themselves have produced, in some way which is not under- 
stood, the glycerin necessary for the synthesis. 4 
Are fats formed from carbohydrate ? — This is a question of great 
practical importance, seeing that carbohydrate foods are the cheapest forms 
of nutriment, and that the fattening of animals is an important branch of 
agricultural industry. The experience of all rearers of animals for market 
points to the fact that carbohydrates do produce fat. Sheep and oxen 
fed purely upon grass, which contains hardly any fat and but little 
proteid in proportion to the carbohydrate present, lay on a large amount 
of fat, and the artificial foods which are used for fattening purposes 
1 Lebedeff, Centralbl. f. d. tried. WUsensch. , Berlin, 1882, S. 129 ; Ztschr. f. physiol. 
Chem., Strassburg, 1882, Bd. vi. S. 149 ; Arch. f. d. ges. Physiol., Bonn, 1883. Bd. xxxi. 
S. 11 ; I. Munk, Arch. f. Physiol, Leipzig, 1883, S. 273 {Verhandl. d. physiol. 
Gesdlsch. zu Berlin) ; Virchov;s Archiv, 18S4, Bd. xcv. S. 407. 
" Radziewski, Virchov/s Archiv, 1868, Bd. xliii. S. 2S6 ; Lebedeff, loc. cit. ; I. Munk, 
loc. cit. See also Minkowski, Arch. f. exper. Path. u. Pharmakol., Leipzig, 1886, Bd. xxi. 
S. 373, and I. Munk and Rosenstein, Virchow's Archiv, 1891, Bd. cxxii. S. 230, for evidence 
that foreign fats pass into the chyle. 
3 See note 2 on next page. 
4 For further details regarding these and similar experiments, see article on "Fat 
Absorption," p. 443. 
