214 PHYSIOLOGICAL CHEMISTRY 



controlled, or influenced by salts. The irritability of muscle and 

 nerve is greatly affected by the kind and amount of salts, pres- 

 ent. The clotting of blood and of milk both are dependent upon 

 the presence of calcium. The general osmotic equilibrium of 

 tissues and fluids depends in large measure upon salts. Even 

 the development of the unfertilized eggs of some animals may 

 be stimulated by certain salts. Evidently the inorganic 

 materials of the body have far more extended importance than 

 merely to form an inert framework to support and protect the 

 soft organs and tissues. 



Osborne and Mendel, in 1918 fed rats on diets which were 

 adequate in every respect except their content of inorganic 

 materials. Various salts were added to this diet. It was found 

 that the omission of chloride, phosphorus, sodium, potassium 

 and magnesium caused the animals to stop growing. Evidently 

 certain salts are necessary for normal growth. It is also well 

 known that a calcium-free diet results in faulty bone formation. 

 Hart, McCollum and Humphrey fed a cow on a diet deficient 

 in calcium. In a little over three months she lost 5.5 Ibs. of 

 calcium from her own body. It is quite evident that an ade- 

 quate supply of inorganic materials must be included in the 

 diet. The ordinary mixed diet of the average adult usually 

 contains these substances in sufficient quantity and diversity. 

 Certain conditions involving faulty bone formation, such as 

 rickets, are not necessarily due to shortage of inorganic materials 

 in the food, however, but to deranged metabolic conditions ; 

 which result in failure on the part of the organism properly 

 to use its available supplies (see discussion of vitamines). 



Energy Exchange, A very important phase of metabolism 

 is concerned with the body's energy requirements. Very amus- 

 ing ideas on this subject prevailed up to a century and a half 

 ago. The foundations of present day knowledge were laid by 

 the great Frenchman, Lavoisier, who demonstrated that there 

 was something in common between the burning of a candle and 

 the breathing of an animal. Mice died and candles went out if 

 placed under a bell jar, and either one shortened the period of 



