INORGANIC ALIMENTARY SUBSTANCES 149 



been so indefinite in their applications to physiology, that its discussion 

 would be out of place in this work. It is sufficient to say that these 

 reactions involve hydrolytic cleavages accelerated by various condi- 

 tions such as elevation of temperature and the presence of acids and 

 enzymes and retarded by others. These changes are thought to be 

 due to the dissociation of water and the action of the hydrogen ion. 1 

 Applications of these ideas to what may be called general metabolic 

 changes in the living body are evident ; and theoretical considerations 

 of this kind might be extended to the digestion of proteids. The 

 hydrolytic changes in carbohydrates have been closely studied and many 

 of them accurately described. It is not too much to say that the most 

 efficient agent in the most important of the digestive, nutritive and 

 katabolic processes probably is dissociated water, its action being 

 favored or retarded by varying conditions. 



Sodium Chloride. Of all saline substances, sodium chloride is the 

 one most widely distributed in the animal and the vegetable kingdoms. 

 It exists in all varieties of food ; but the quantity taken in combination 

 with other matters usually is insufficient for the purposes of the economy, 

 and common salt is added to certain articles of food as a condiment, 

 when it improves their flavor, promotes the secretion of certain of the 

 digestive fluids and meets a nutritive demand. Experiments and obser- 

 vations have shown that a deficiency of sodium chloride in food has an 

 unfavorable influence on the general processes of nutrition. 



Calcium Phosphate. This is almost as common a constituent of 

 vegetable and animal food as sodium chloride. It is seldom taken except 

 in combination, particularly with nitrogenous alimentary matters. Its 

 importance in alimentation has been experimentally demonstrated, it 

 having been shown that in animals deprived as completely as possible 

 of this salt, the nutrition of the body, particularly in parts that contain 

 it in considerable quantity, as the bones, is seriously affected. 



Iron. Hemoglobin, the coloring matter of the blood, contains, inti- 

 mately united with organic matters, a certain proportion of iron. Ex- 

 amples of simple anemia, which are frequently met with in practice and 

 are almost always relieved in a short time by the administration of iron, 

 are evidences of the importance of this substance in alimentation. 

 The quantity of iron discharged from the body is slight, only a trace 

 being discoverable in the urine. A small quantity of iron frequently is 

 introduced in solution in the water taken as drink, and it is a constant 

 constituent of milk and eggs. When its supply in the food is insufficient, 

 it is necessary, in order to restore the normal processes of nutrition, to 



1 A very lucid exposition of the action of the hydrogen ion in catalysis is given by Jones, in 

 " The Elements of Physical Chemistry," New York, 1902, p. 456. 



