CHEMICAL BASIS OF THE ANIMAL BODY. 1235 



from this by taking advantage of the varying solubilities of the 

 zinc salts of the two acids. 



More recent researches have however made it probable that 

 what has usually been described as ethylene-lactic acid, 

 obtainable from muscle-extract, is really acetyl-lactic acid, 

 CH 3 . CH(C 2 H 3 O 2 ) COOH, the true ethylene-lactic acid being 

 hydracrylic acid, which does not occur in the animal body, 



Hydroxy-butyric acid. CH 3 . CH(OH) . CH 2 . COOH. 



This acid is the next homologue to the lactic acids in the 

 glycolic series. It is frequently found in the urine of acute 

 diabetes, usually accompanied by aceto-acetic acid [CH 3 . CO . 

 CH . COOH]. The pure acid is sirupy and laevorotatorv, 

 (a) D =-23-4. 







OXALIC ACID SERIES. 

 Oxalic acid. (CO . OH) 2 . 



This acid does not occur in the free state in the human 

 body. Calcium oxalate, however, is a not unfrequent constitu- 



FIG. 198. CALCIUM OXALATE. (After Funke.) 



ent of urine, and enters into the composition of many urinary 

 calculi, the so-called mulberry calculus consisting almost en- 

 tirely of it, and it is very commonly found in urinary deposits. 

 As ordinarily precipitated from solutions of calcium salts 

 by the addition of a salt of oxalic acid, the calcium oxalate 

 is usually amorphous. To obtain it in the crystalline form 

 dilute solutions of the two reagents must be allowed to mix 

 very slowly, as by diffusion. In urine the case is different; 

 the oxalate is at first in dilute solution, probably dissolved 

 by the sodium dihydric phosphate (NaH 2 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. 



In some cases it presents the anomalous forms of rounded 

 lumps, dumb-bells, or square columns with pyramidal ends, 

 but these forms are uncommon. 



