22 TEXT-BOOK OF PHYSIOLOGY 



essential to physiologic action that all tissue elements should be bathed by 

 an alkaline medium. 



Sodium carbonate, Na 2 CO s , is generally found in association with the 

 preceding salt As it is an alkaline compound, it also assists in giving to 

 the blood and lymph their characteristic alkalinity. In carnivorous animals 

 the sodium phosphate is the more abundant, 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, however, in the 

 tissue elements, especially in the muscle tissue, nerve tissue, and red cor- 

 puscles. The plasma with which these structures are bathed contains but a 

 very small amount of this salt, but, as previously stated, a relatively large 

 amount 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 so- 

 dium 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 preceding 

 salt. 



MAGNESIUM COMPOUNDS. 



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

 tion with calcium phosphate, though in much smaller quantity. 



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



IRON COMPOUNDS. 



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

 ever, 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 70 

 kilograms is about 2.2 gm. It exists under various forms e.g., ferric oxid, 

 and in combination with organic compounds. 



lodin is found in a number of organs thyroid gland, lungs, ovaries, 

 liver, hypophysis, small intestines as well as in the blood and bile. The 

 iodine content of the thyroid gland is eight to ten times that of all the other 

 organs. The active ingredient of the thyroid colloid is the iodin-con taming 

 substance called thyroidin. It is contained in that portion of the protein 

 which is soluble in physiological salt solution and precipitated upon half 

 saturation with ammonium sulphate. This portion is apparently a globulin 

 called thyreoglobulin, and contains an easily separated carbohydrate group. 

 The thyroid glands of new-born children are iodin free. 



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 characteristic pro- 

 portions, to form compounds whose properties are the resultant of those of 



