( HKMICAL BASIS OF THE ANIMAL BODY. 131 



sodium. The above characteristics serve to identify this salt, 

 but in practice the microscopical appearance is usually of most 

 use. 



Succinic acid. COOH . CH, . CH 2 . COOH. 



This is the- third acid of the oxalic series, being separated from 

 oxalic acid by the intermediate malonic acid, CH.(COOH) 2 . It 

 may occur in the spleen, the thymus, and thyroid bodies, hydro- 

 cephalic and hydrocele fluids. It has also been stated to occur 

 normally in urine, but this is very doubtful, 1 as also is the state- 

 ment that it is found in this excretion after taking food rich in 

 asparagin, e. g. asparagus. 2 It is obtained as a product of the 

 putrefaction of proteids. 3 



Succinic acid crystallises most usually in the form of large 

 four-sided prisms, occasionally as rhombic tables. It is soluble 

 in about 20 parts of cold water, much more so in hot ; it is also 

 soluble iii alcohol, more especially if hot, and is but very slightly 

 so in ether. 



The crystals melt at 180 C., and boil at 235 C., being at the 

 same time decomposed into the anhydride and water. The 

 alkali salts of this acid are soluble in water, insoluble in alco- 

 hol and in ether. 



Preparation. Apart from the synthetic methods, it may 

 n-adily be obtained by the fermentation of malic* or tartaric 6 

 acids, which are closely related to succinic, the former being 

 hv.lroxy-succinic, COOH. CH 2 .CH(OH). COOH, and the latter 

 dihydroxy-succinic acid, COOH. CH(OH) .CH(OH) . COOH. 



Some of the amido-derivatives of succinic acid, viz. asparagin 

 and asjiartic acid, are of considerable interest; they will be 

 described later on. 



Cholesterin. C 26 H 44 or C, 6 H 42 0. e 



This substance is described here rather for the sake of conveni 

 ence than from its possessing any relationship to those which have 

 preceded it. 



Cholesterin is the only alcohol which occurs in the human 

 body in the free state. (The triatomic alcohol glycerin is al- 

 ways found combined as in the fats ; and cetyl-alcohol is ob- 



Salkowski, PflOger'B Arch. Bd. iv. (1871), S. 94. 



v I u ,), /j. r. ;iA.yof. Chen. Bd. I. (1877), S. 213. 



Salkf.w;ki. K.'u. H'., Ber. d. d. them. Getell. 1880, 8. 189. 

 I.iobig, Ann. d. Chem. u. Pharm. Bd. LXX. (1849), Sn. 104, 363. 

 Konip, Ber. d. d. ehem. Griell. 1882, S. 172. 



Howe. Ann. d. Chrm. u. Pharm. Bd. cxcn. (1878), S. 175. Schulze u. Barbieri, 

 Jn. f. pnd-t. Chem. Bd XXV. (1882), Sn. 159, 458. 



