206 UNCONSCIOUS NERVOUS OPERATIONS 



in proportion to the increase of muscular effort. Carbo- 

 hydrates cannot alone form tissue, but under some circum- 

 stances may be used for that purpose with other elements. 



293. Water, composed of oxygen and hydrogen, is found 

 in all foods, and has a variety of uses in connection with 

 nutrition, partly as a solvent for various elements in the 

 food, and partly as promoting osmosis, and as an aid to 

 the varied changes which take place in the tissues. Water 

 uncombined with food, introduced into the stomach as in 

 drinking, is all absorbed directly into the blood, of which 

 it forms about 80 per cent. 



294. Salts. The food elements that are salts are chiefly 

 the chlorides, phosphates, and carbonates of sodium and 

 potassium, and to a less extent those of calcium and mag- 

 nesium, with salts of iron and of some of the organic acids. 

 Common salt (chloride of sodium) appears in all animal 

 bodies, and to some extent in plants also. It helps to dis- 

 solve certain of the albumins of the body, promotes the flow 

 of the digestive fluids, and aids digestion in various ways. 

 About half an ounce each day is needed with the food. 

 That these saline matters are essential to health, is proved 

 by experiments upon animals. When they are eliminated 

 so far as possible from the diet, the central nervous sys- 

 tem soon suffers, and paralysis results, besides general 

 derangement of nutrition. When an animal body is 

 burned, the various salts which entered into its composi- 

 tion appear in the ashes which are left, while the other sub- 

 stances have been changed into gases. 



295. Food Accessories. These are the various drinks 

 alcohol in different forms, tea, coffee, cocoa, etc. ; and condi- 

 ments mustard, pepper, ginger, and other spices, and a 

 variety of other flavors added, not for their food value 

 (though of that they may have a small amount), but to give 



