CHEMICAL BASIS OF THE ANIMAL BODY. 893 



As ordinarily precipitated from solutions of calcic salts by ammonic oxalate, 

 calcic oxalate is quite amorphous, but in urinary deposits it assumes a strong cha- 

 racteristic crystalline form, viz., that of rectangular octohedra [Fig. 233]. In some 

 cases it presents the anomalous forms of rounded lumps, dumb-bells, or square 

 columns with pyramidal ends. It is insoluble in water, alcohol, and ether, also in 

 ammonia and acetic acid. Mineral acids dissolve this salt readily, as also to a smaller 

 extent do solutions of sodic phosphate or urate. All the above characteristics serve 

 to detect this salt ; its microscopical appearance, however, is generally of most use 

 for this purpose. 



The pure acid is prepared either by oxidizing sugar with nitric acid, or decom- 

 posing ligneous tissue with caustic alkalies. 



Succinic Acid. H 2 C 4 H 4 4 . 



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

 the intermediate malonic acid, H. 2 C 3 H 2 4 . It occurs in the spleen, the thymus, 

 and thyroid bodies, hydrocephalic and hydrocele fluids. 



According to Meissner and Shepard l it is found as a normal constituent of urine. This is con- 

 tested by Salkowski, 2 and also by v. Speyer. It seems probable, however, that since wines and 

 fermented liquors contain succinic acid, and this latter passes unchanged into the urine, that it 

 may thus be occasionally present in this excretion. 



Succinic acid crystallizes in large rhombic tables, also at times in the form of 

 large prisms; they are soluble in 5 parts of cold water, and 2.2 of boiling, slightly 

 soluble in alcohol, and almost insoluble in ether. The crystals melt at 180 C., 

 and boil at 236 C. , being at the same time decomposed into the anhydride and 

 water. The alkali salts of this acid are soluble in water, insoluble in alcohol and 

 ether. 



Preparation. Apart from the synthetic methods, it may readily be obtained by 

 the fermentation of calcic malate, acetic acid being produced simultaneously. 



Its presence is recognized by the microscopic examination of its crystals, and 

 its characteristic reaction with normal lead acetate. With this it gives a precip- 

 itate, easily soluble in excess of the precipitant, but coming, down again on warm- 

 ing and shaking. 3 



CHOLESTERIN. (C 26 H 44 0.) 



This is the only alcohol which occurs in the human body in the free state. 

 (The triatomic alcohol glycerin is almost always found combined as in the fats ; 

 and cetyl-alcohol, or sethal, is obtained only from spermaceti. ) It is a white crys- 

 talline body, crystallizing in fine needles from its solution in ether, chloroform, or 

 benzol ; from its hot alcoholic solutions it is deposited on cooling in rhombic 

 tables [Fig. 234]. When dried it melts at 145 C., and distils in closed vessels at 

 360 C. It is quite insoluble in water and cold alcohol : soluble in solutions of bile 

 salts- 

 Solutions of cholesterin possess a left-handed rotatory action on polarized light, 

 of 32 for yellow light, this being independent of concentration and of the nature 

 of the solvent. 



Heated with strong sulphuric acid it yields a hydrocarbon ; with concentrated 

 nitric it gives cholesteric acid and other products. It is capable of uniting with 

 acids and forming compound ethers. 



Cholesterin occurs in small quantities in the blood and many tissues, and is pres- 

 ent in abundance in the white matter of the cerebro-spinal axis and in nerves. 



It is a constant constituent .of bile, forming frequently nearly the whole mass of 

 some gall-stones. It is found in many pathological fluids, hydrocele, the fluid of 

 ovarian cysts, etc. 



Preparation. From gall-stones by simple extraction with boiling alcohol, and 

 treatment with alcoholic potash to free from extraneous matter. 



As tests for this substance may be given : With concentrated sulphuric acid and 

 a little iodine a violet color is obtained, changing through green to red or blue. 

 This is applicable to the microscopic crystals. After dissolving in chloroform a 

 blood-red solution is formed on the addition of an equal volume of concentrated 



1 Untersuch, viber d. Entsteh. d. Hippursaiire. Hanover, 1866. 



2 Pfliiger's Archiv, Bd. ii. (1869), S. 367, and Bd. iv. (1871), S. 95. 



8 For further particulars see Meissner, op. cit., and Meissner and Solly, Zeitschr f. rat. (Med. 3). 

 B. xxiv., S. 97. 



