968 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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 is 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. 959). 



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

 CaH 2 (CO 3 ) 2 , and the secondary or neutral carbonate, CaCO 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 (PO 4 ) 6 , or 3Ca 3 (PO 4 ) 2 ,CaCO 3 , in which CO 3 has the position 

 of F 2 in apatite. In the wasting of the mineral matter of bones in osteoma- 

 lacia this formula of composition remains constant/ 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 (CO 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 

 is 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 and fibrin 

 always contains calcium. If ten parts of blood be drawn into one part of a 

 1 per cent, solution of potassium oxalate, thus precipitating the calcium, no 

 coagulation takes place, but on the addition of calcium chloride a typical fibrin 

 forms. A solution of sodium oxalate passed through a beating excised heart 

 causes it to cease beating 3 and nerves and muscles lose their irritability when 

 calcium salts are abstracted from them with sodium oxalate. 4 These facts 

 illustrate the intimate relation between calcium salts and the functional activity 

 of protoplasm. 



Detection. Ammonium oxalate in neutral or alkaline solutions of calcium 

 salts gives a precipitate of calcium oxalate a white powder, insoluble in acetic 

 or oxalic acid. 



1 M. Levey: Zeitschrift fur physiologische Chemie, 1894, Bd. 19, p. 239. 



2 Arthus et Paget : Archives de Physiologie, vlo. ii. p. 739. 



3 Howell and Cooke : Journal of Physiology, 1893, vol. 14, p. 219, note. 



4 Howell : Journal of Physiology, 1894, vol. 16, p. 476. 



