THE CHEMISTRY OF THE ANIMAL BODY. 523 



gastric juice than one not so mixed. Sodium carbonate may be obtained for 

 the body either directly from the food by absorption, or indirectly through 

 combustion of sodium organic salts. Ingested in sufficiently large quantities, 

 it makes the urine alkaline. 



Sodium salts are undoubtedly united with serum-albumin in the plasma, 

 forming a combination which may be dissociated by carbonic oxide. 



Sodium gives a yellow coloration to a colorless flame, and a distinctive bright line in the 

 yellow of the spectroscope. 



Sodium in the Body. — This subject has been discussed under the different salts, and 

 likewise under potassium and hydrochloric acid ; repetition here is therefore needless. 



Ammonium, NH 4 . 



Ammonia, NH 3 , has already been described (p. 511). 



Sodium-Ammonium Phosphate, NaNH 4 HP0 4 , is an insoluble salt formed in the 

 urine during ammoniacal fermentation. 



Ammonium Carbonate, (NH 4 ) 2 C0 3 , is formed by the union of carbonic 

 oxide and ammonia in the presence of water, and is therefore a usual product 

 of putrefaction. If introduced into the blood, it is converted into urea by the 

 liver. In uremia urea passes from the blood into the stomach and is there 

 converted into ammonium carbonate, which produces vomiting through irrita- 

 tion of the mucous membrane. (See further discussion under Carbamic Acid 

 and Urea.) 



Calcium, Ca = 40. 



Calcium is by far the most abundant metallic element in the body, and, as 

 has been found in the dog, 99.5 per cent, belongs to the composition of the 

 bones. 1 Outside the bones it occurs most abundantly in blood-plasma. It is 

 found in all the cells and fluids of the body, probably loosely combined with 

 proteid. Calcium is always accompanied by magnesium. 



Calcium Chloride, CaCl 2 , is found in small quantities in the bones. 



Calcium Fluoride, CaF 2 , a salt insoluble in water, is found in bone, den- 

 tine, and enamel (see p. 510). 



Calcium Sulphate, CaS0 4 , is found in small quantities in bones and rarely 

 as part of the sediment in strongly acid urine. 



Calcium Phosphates. — Of these there are three — primary, CaH 4 (P0 4 ) 2 , 

 secondary, CaHP0 4 , and tertiary, Ca 3 (P0 4 ) 2 . The tertiary phosphate is insol- 

 uble in water, the secondary only very slightly soluble, but the primary salt is 

 soluble. The tertiary and secondary phosphates are insoluble in alkali, but 

 soluble in mineral acids and in acetic acid. The tertiary phosphate forms the 

 largest mineral constituent of the bones (83.89 per cent., Zalesky) and of den- 

 tine and enamel. Tertiary phosphate of calcium likewise occurs in the blood; 

 how it is held in solution it is difficult to say, though it is probably loosely 

 combined with proteid. In a similar way it is combined with the protoplasm 

 of the cell. It is largely found in the ash of milk, having been in previous 

 chemical combination with casein. Tertiary phosphate of calcium is continu- 

 1 Ileiss: Zeitschriftfiir Biologie, 1876, Bd. 12, S. 165. 



