CHEMIC COMPOSITION OF THE HUMAN BODY. 39 



while in the herbivorous animals the sodium carbonate is the more 

 abundant. 



Sodium sulphate, Na 2 SO 4 , is present in many of the tissues and 

 fluids, especially in the urine. Though introduced in the food, it is 

 also, in all probability, formed in the body from the decomposition 

 and oxidation of the proteids. 



POTASSIUM COMPOUNDS. 



Potassium chlorid, KC1, is met with in association with sodium 

 chlorid in almost all situations in the body. It preponderates, how- 

 ever, in the tissue elements, especially in the muscle tissue, nerve 

 tissue, and red corpuscles. The plasma with which these structures 

 are bathed contains but a very small amount of this salt, but, as 

 previously stated, a relatively large quantity of sodium chlorid. 

 Though introduced to some extent in the food, it is very likely that 

 it is also formed through the decomposition of the sodium chlorid. 



Potassium phosphate, K 2 HPO 4 , is found in association with 

 sodium phosphate in all the fluids and solids. As it has similar 

 chemic properties, its functions are practically the same. 



Potassium carbonate, K 2 CO 3 , is generally found with the pre- 

 ceding salt. 



MAGNESIUM COMPOUNDS. 



Magnesium phosphate, Mg 3 (PO 4 ) 2 , is found in all tissues, in 

 association with calcium phosphate, though in much smaller quantity. 



Magnesium carbonate, MgCO 3 , occurs only in traces in the 

 blood. 



Both of these compounds have functions similar to the calcium 

 compounds, and exist, in all probability, under similar conditions. 



IRON COMPOUNDS. 



Iron is a constituent of the coloring-matter of the blood. Traces, 

 however, are also found in lymph, bile, gastric juice, and in the 

 pigment of the eyes, skin, and hair. The amount of iron contained 

 in a body weighing 75 kilograms is about 3 gm. It exists under 

 various forms e. g., ferric oxid, and in combination with organic 

 compounds. 



Chemic analysis thus shows that the chemic elements into which 

 the compounds may be resolved by an ultimate analysis do not exist 

 in the body in a free state, but only in combination, and in char- 

 acteristic proportions, to form compounds whose properties are the 

 resultant of those of the elements. Of the four principal elements 

 which make up 97 per cent, of the body, O, H, N are extremely 

 mobile, elastic, and possessed of great atomic heat. C, H, N are 

 distinguished for the narrow range of their affinities, and for their 



