438 MAMMALIA— PHYSIOLOGY 



the formation of tissues. The mineral salts are necessary to main- 

 tain normal physiological equilibrium and purposeful activity in the 

 organism. 



Sulphur is absorbed by plants and used in the manufacture of 

 some amino-acids. Phosphorus is essential to the formation of 

 nuclein and lecithin of living cells. Calcium salts are necessary in 

 the coagulation of blood and milk. Apparently the normal beating 

 of the heart depends on the relationship of calcium to sodium and 

 potassium salts. The condition known as rickets is due to a failure 

 to maintain the proper ratio between the calcium and phosphates of 

 the food. Cod liver oil is a cure for rickets (see page 443, Vitamin 

 D). Silicon and fluorine are required in small quantities for the 

 proper formation and growth of bones and teeth. They are secured 

 from milk and fibrous vegetables. The ash of hair shows 40 per cent 

 of silicon dioxide. Sodium as NaCl is essential to herbivorous 

 animals, but the carnivores do not take salt. Raw meat protects 

 the Greenland Eskimo from scurvy, rickets, and avitaminosis. 



Chlorine is important to the animal in maintaining the secretion 

 of gastric juice and in keeping the optimum osmotic pressure. The 

 acid-secreting cells of the stomach select for their use the NaCl of the 

 blood. Potassium salts are indispensable in the synthetic processes 

 of organic combination. They aid in the formation of glycogen 

 from glucose, of fats from glycogen and of proteins from peptones. 

 The liver, the source of glycogen, contains twice as much potassium 

 as sodium. Potassium is found in red blood corpuscles and also in 

 the brain and is apparently necessary to the normal function of 

 organic life. Magnesium is found in greater quantity than calcium 

 in the muscular tissues and the nervous system. The salts of 

 magnesium aid in the formation of the albumin of the blood, reduce 

 foreign matter and waste and maintain the osmotic pressure of the 

 blood. Irradiation with ultra-violet light is said to decrease the 

 magnesium content of rats. Magnesium requires the presence of 

 calcium salts for proper function and is in fact injurious in the ab- 

 sence of calcium. An excess of magnesium in the blood is said to 

 cause glycosuria. Magnesium has been proved necessary for the 

 growth and maintenance of white mice. The chlorophyll of green 

 plants is always associated with magnesium. Copper.^ found in the 

 earth in metallic form, occurs in minute quantities in most vegetable 

 and animal tissues. It 7nay act as a catalyzer in the production of 

 hemoglobin. 



