CHEMICAL BASIS OF THE ANIMAL BODY. 123 



but indirectly by protecting the proteids from the metabolism they 

 would otherwise have undergone. According to this view fat is formed 

 from proteids only. Lawes and Gilbert on the other hand took the 

 view that carbohydrates are directly converted into fat. While there 

 is no doubt that proteids can give rise directly to fat as shown by 

 the storage of fat during "nitrogenous equilibrium" (see 522), 

 there is also now equally no doubt that carbohydrates can lead to a 

 direct storage of fat by being themselves converted into fat. This is 

 the incontrovertible outcome of the most recent experiments, which 

 have proved that with a diet rich in carbohydrates, so that the storage 

 of fat is sufficiently rapid, more fat is laid on than could possibly have 

 been formed from the proteids in the food given l . 



Glycerin (Glycerol). C 3 H 5 (OH) 3 . 



As already stated, glycerin is a triatomic alcohol, the neutral fats 

 being ethereal salts formed from it with the radicles of the higher fatty 

 acids and oleic acid. 



When pure, glycerin is a viscid, colourless liquid, of a well-known 

 sweet taste. It is soluble in water and in alcohol in all proportions, 

 insoluble in ether. Exposed to very low temperatures it becomes almost 

 solid ; it boils at 290 and may be distilled without decomposition 

 in the absence of air. 



It dissolves the alkalis and alkaline earths, also many oxides, such 

 as those of lead and copper ; many of the fatty acids are also soluble in 

 glycerin. 



It possesses no rotatory power on polarised light. 



It is easily recognized by its ready solubility in both water and alcohol, 

 its insolubility in ether, its sweet taste, and its reaction with bases. 

 When sufficiently heated, especially in presence of a dehydrating agent, 

 glycerin is decomposed, loses two molecules of water and yields acrolein. 

 C 3 H 5 (OH) 3 ^C 3 H 4 O + 2H 2 O. This substance possesses an intensely 

 penetrating, irritating and pungent odour so that its formation enables 

 glycerin to be readily identified. It is the cause of the peculiar smell 

 arising from overheated fats. Chemically it is the aldehyde of allyl 

 alcohol (derived from the olefines) and is intermediate between this 

 substance and acrylic acid, which is a homologue of oleic acid. (See 

 above.) 



Glycerin is formed in traces during the alcoholic fermentation of 



1 Meissl u. Stvohmer, Sitzb. d. Wien. Akad. Bd. LXXXVIII. 1883, HI. Abth. July. 

 Tscherwinsky, Landwirth. Versuchsstat. Bd. xxix. (1883), S. 317. Chaniewski, Zt. 

 /. Blol. Bd. xx. (1884), S. 179. Buhner, Ibid. Bd. xxn. (1886), S. 272. Munk, 

 Virchow's Arch. Bd. ci. (1885), S. 91. Biol. Centralb. Bd. v. (188586), S. 316. 

 See also Voit, Ibid. Bd. vi. (188687), S. 243. 



