ELEMENTS OF COMPOSITION. 35 



24. 



Two other acids, from another series occurring in the human body 

 must now be considered, namely, oxalic and succinic. 



Oxalic Acid, C 2 2 (OH) 2 . 



This acid is found widely throughout the vegetable kingdom, and ap- 

 pears as an end product in the oxidation of most animal and vegetable 

 substances. Oxalic acid forms with one atom of Ca neutral oxalate of 

 calcium, almost the only one of its salts found in the human body. 



Oxalate of Calcium, C 2 4 Ca + 3H 2 . 



This compound is insoluble in water and acetic acid, but soluble in 

 hydrochloric and nitric acids. On being roasted it is converted into car- 

 bonate of calcium. It crystallises in blunt, and at times also pointed, square 

 octahedrons, which look like envelopes under low micro- 

 scopic power (fig. 11). 



Oxalate of calcium, a large amount of which is never met with 

 in the body, is probably, in very minute quantity, a normal 

 constituent of the urine. After a vegetable diet, and drinks 

 containing a large amount of carbonic acid, this salt has been 

 most frequently observed. It likewise appears in conjunc- 

 tion with disturbance of the respiratory functions, and may 

 give rise to the formation of mulberry calculi. It is, further, 

 met with in the gall-bladder and in uterine mucus (G. 



Schmidt). ofcalcium. 



The sources of oxalic acid may be manifold, as is indicated by its occur- 

 rence and origin. In the first place, it may spring from vegetable food, 

 and, in the second, from the decomposition of various animal matters. In 

 the latter respect its formation from the oxidation of uric acid must be 

 mentioned ( Wohler and Liebig) ; also the fact that, on the injection of 

 mates into the blood, the amount of urea and oxalic acid is increased in 

 the urine ( Wohler and Frerichs). 



Succinic Acid, C 4 H 6 4 . 



This compound, which originates in the oxidation of the fatty acids, 

 as well as from the fermentation of different organic acids, crystallizes in 

 colourless monoclinometric prisms (fig. 12), 

 and is soluble in water and alcohol. 



It was formerly supposed to occur, as has 

 been already mentioned, only as a patholo- 

 gical constituent of the body, in encysted 

 tumours and dropsical fluids, until demon- 

 strated by Gomp-Besanez in a number of 

 gland-juices, namely, those of the spleen, 

 thymus, and thyroid. It has been, like- 

 wise, met with by Me'tssner and Shepard in Fig ' 12 - Cr >'stais of succinic add. 

 the blood of phytophagous mammals, in human urine, and that of both 

 carnivora and vegetable feeders, after fatty diet or the reception into the 

 system of malic acid (Meissner, Koch). 



