THE FATS. 221 



according to Liebig,* the formation of fat from sugar may be 

 explained in two different ways. It may in the one case be analo- 

 gous with vinous fermentation, or with the formation of fusel oil, 

 the atom of sugar being decomposed into carbonic acid, and into a 

 substance poor in oxygen ; or in the other case, the sugar may 

 undergo a process analogous with the butyric fermentation, by means 

 of which the hydrogen is in part abstracted from the carbo-hydrate, 

 and carbonic acid escapes, while a substance poor in oxygen 

 remains in the form of one of the known fatty acids. In the 

 butyric fermentation, one atom of sugar is decomposed into hydro- 

 gen, carbonic acid, and butyric acid (C 12 H 12 O 12 =4H+4CO 2 + 

 C 8 H 7 O 3 . HO) ; in the formation of caprylic acid within the animal 

 body, two atoms of sugar become decomposed into the above- 

 named acid, carbonic acid and hydrogen, the latter combining to 

 form water with the oxygen which it meets with in the blood 

 (C 24 H 24 O 25 + 4O=4HO + 8 CO 2 -f C 16 H 15 O 3 .HO). Liebig ad- 

 duces an interesting experiment in support of the view to which 

 we have already referred, that the formation of fat is effected in 

 the liver. When pieces of calves 5 liver are chopped up in water, 

 and suffered to stand at a temperature of 39 or 40, an extraor- 

 dinary amount of pure hydrogen gas will be developed in about 

 four or five hours ; some ferment must, therefore, be developed 

 here, which is capable of separating the hydrogen from the 

 oxygen. In every case the deposition of fat within the animal 

 body betrays a certain deficiency of oxygen, showing that the 

 amount of oxygen respired was insufficient to allow the complete 

 separation of the sugar into water and carbonic acid. 



The part taken by the fats in the metamorphosis of animal 

 matter has already been very fully considered in the first volume. 

 We there showed (after discussing the mechanical objects fulfilled 

 by the fats in different parts of the animal body), that these sub- 

 stances accomplish definite purposes in the primse viae, and that 

 they appear to be powerful auxiliaries in the formation of cells and 

 tissues, whilst their ample supply of carbon and hydrogen, and their 

 gradual oxidation, enable them to contribute essentially towards 

 the generation of animal heat. We shall refer in a future page to 

 the special value of the fats in relation to the generation of heat. 



We now pass to another group of substances, whose occurrence 

 in the body, and whose importance in the animal economy have 

 already been considered in detail in the first volume of the present 



* Thierchemie. 1846, S. 102. Chemische Briefe. 1851, S. 486-492 [or 

 Letters on Chemistry. London, 1851, p. 377.] 



