CHEMICAL BASIS OF THE ANIMAL BODY. 131 



first in dilute solution, probably dissolved by the sodium dihydric phos- 

 phate (NaH PO 4 ) to which the acidity is normally due. On standing 

 the urine cools and the oxalate separates out in a crystalline form, viz, 

 rectangular octohedra, which is characteristic and striking, and usually 

 unlike that of any other constituent of urinary deposits. 



FIG. 4. CALCIUM OXALATE. (After Funke.) 



In some cases it presents the anomalous forms of rounded lumps, 

 dumb-bells, or square columns with pyramidal ends, but these forms are 

 uncommon. 



The crystals are insoluble in ammonia and acetic acid, but readily 

 soluble in hydrochloric or other mineral acid, also slightly so in solutions 

 of ,cid phosphates and urates of sodium. The above characteristics 

 serve to identify this salt, but in practice the microscopical appearance 

 is usually of most use. 



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



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

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

 occur in the spleen, the thymus, and thyroid bodies, hydrocephalic and 

 hydrocele fluids. It has also been stated to occur normally in urine, 

 but this is very doubtful 1 , as also is the statement 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 in 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 alcohol and in ether. 



1 Salkowski, Pfliiger's Arch. Bd. iv. (1871), S. 94. 



2 v. Longo, Zt. /. physiol. Chem. Bd. i. (1877), S. 213. 



3 Salkowski, E. u. H., Ber. d. d. diem. Gesell. 1880, S. 189. 



