MAMMALIA— PHYSIOLOGY 437 



also formed from carbohydrates and proteins. Fats contain twice 

 as much heat energy as carbohydrates and are essential in maintain- 

 ing the proper body temperature. 



Substances that contain at some point in the chain two carbon 

 atoms united by more than one bond are said to be " unsaturated," 

 and are able to form additive compounds with the halogens chlorin, 

 bromin, and iodin. The " iodin number " of an oil or fat is a meas- 

 ure of its ability to absorb iodin. Unsaturated fats act antienzy- 

 matically, and undoubtedly function in the animal body in taking 

 up iodin. Excess fat in the diet may predispose to goiter. 



Experiments by Chidester and associates have indicated the 

 importance of unsaturated fatty acids in the treatment of Vitamin A 

 deficiency, when combined with ferrous iodide. The author is also 

 continuing experiments with the idea that the efficacy of wheat 

 germ oil, hempseed and other oils used in the recovery of animals 

 deficient in Vitamin E is in part due to their highly unsaturated 

 condition. The degree of unsaturation decreases rapidly in seeds 

 during their period of germination. Cocoanut oil has a high degree 

 of saturation, and is ineffective. 



Chemical Elements of Protoplasm. — Carbon compounds are the 

 primary materials of protoplasm. Carbon unites with oxygen to 

 form carbon dioxide and water and to liberate energy. 



Hydrogen is taken into the bodies of plants and animals in com- 

 bination with oxygen as water and is also excreted in this form. 

 Oxygen is found in the free state and unites with various compounds 

 of protoplasm, the process of oxidation, releasing energy. 



Nitrogen is essential to protoplasm. It forms 79 per cent of the 

 atmosphere. Taken into plant bodies usually in the form of 

 nitrates, the plants utilize it in the manufacture of proteins. Am- 

 monia, a nitrogen compound, formed in the catabolism of plants and 

 animals, is changed by certain bacteria into nitrates which are then 

 absorbed by plants. 



Mineral Salts. — Proteins, carbohydrates, and fats are not the 

 chief foods of man. The most important foods are mineral salts, 

 water and air.^ If mineral salts are withheld from the body, death 

 ensues much more quickly than from the withholding of proteins, 

 carbohydrates, and fats. The salts of the body in solution aid in 

 providing the proper medium for living tissues while those in com- 

 bination with organic substances furnish the proper elements for 



^ Of course not all food constituents necessary to man have been evaluated. 



