524 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



ously excreted into the intestinal tract. It is present in the acid gastric juice, 



bill only in traces in the alkaline saliva, pancreatic jnice, and in the nearly 

 neutral bile. Tertiary phosphates never occur in the urine, except as a sedi- 

 ment after the urine has attained an alkaline reaction, being formed from the 

 acid phosphates. In carnivorous urine the calcium present occurs as primary 

 and secondary phosphate, the solution of the latter being aided by the primary 

 alkali phosphate and sodium chloride. Occasionally a coat is noticed on the 

 surface of the urine, an appearance once thought to be a sign of pregnancy. 

 This coat i- now known to consist chiefly of secondary phosphate of calcium, 

 which may crystallize out on the urine becoming alkaline. Calcium does not 

 occur as phosphate in an alkaline urine (see p. 515). 



Calcium Carbonates. — Of these there are two, the primary or acid, 

 CaH 2 (CO s ) 2 , and the secondary or neutral carbonate, CaC0 3 . Neutral calcium 

 carbonate is the substance of which sea shells, coral, egg-shell, and otoliths 

 consist. It is found in the ash of bones to the extent of 13.032 per cent. 

 (Zalesky). Apatite is a mineral having the formula Ca 10 F 2 ^PO 4 ) 6 , and Hoppe- 

 Seyler, using Zalesky's figures, believes that bone has a composition repre- 

 sented by Ca 10 CO 3 (Pb 4 ) 6 , or 3Ca 3 (P0 4 ) 2 ,CaC0 3 , in which CO a has the position 

 of F in apatite. In the wasting of the mineral matter of bones in osteoma- 

 hh-'m this formula of composition remains constant, 1 one molecule of calcium 

 carbonate always being removed for every three molecules of the phosphate. 

 Neutral calcium carbonate is insoluble in water or alkali, but dissolves in 

 water containing carbonic oxide to form the soluble acid carbonate, CaH 2 (C0 3 ) 2 . 

 This is found in blood and lymph, and in minute quantities in all the tissues. 

 It is found in herbivorous urine, which contains carbonic acid in excess, but it 

 i- soon deposited as neutral carbonate as the carbonic oxide diffuses into the 

 air. It occurs in all alkaline and neutral urines, though to a less extent than 

 calcium phosphate in acid urines. It is found in pancreatic juice and in the 

 saliva, from which latter is derived the calcic carbonate which, mixed with 

 bacteria and other organic matter, is deposited as tartar on the teeth. 



The ferment rennet does not act in the absence of calcium salts. The 

 coagulation of the blood requires the presence of calcium salts. 2 If ten parts 

 of Mood be drawn into one part of a 1 per cent, solution of potassium oxa- 

 late, thus precipitating the calcium, no coagulation takes place, but on the 

 addition of calcium chloride a typical fibrin forms. According to Ilammar- 

 sten, 3 calcium is only necessary in the formation of the ferment. He lias 

 prepared fibrin containing only a trace (0.007 per cent.) of calcium. A solu- 

 tion of sodium oxalate passed through a beating excised heart causes it to 

 cease beating,' and nerves and muscles lose their irritability when calcium 

 salts are abstracted from them with sodium oxalate/' These facts illustrate 



1 M. Levy: Zeilschrift fur phyziologische Chnnie, 1894, Bd. 19, S. 239. 



2 Arthus et Paget: Archives <l>> Physiologie, 1890, p. 739. 



5 Hamtnarsten : Zetiachrifl fur physiologische Chemie, 1899, Bd. 28, S. 90. 



4 Bowel! and Cooke: Journal of Phi/xiology, 1893, vol. 14, p. 219, note. 



5 Howell : Ibid., 1894, vol. 16, p. 47<:. 



