THE INTAKE OF MATERIALS AND ENERGY 61 



Riboflavin (vitamin B 2 or G, C17H20N4O8) is a yellow pigment found in many 

 animal and plant tissues, and especially in yeast, milk, liver, wheat germ, eggs, 

 cheese, green vegetables, and the muscles of animals. On account of its wide 

 distribution riboflavin deficiencies are not common, but when they do occur, 

 normal nutritional and growth processes are upset. The symptoms are varied and 

 none is wholly characteristic. Riboflavin plays an essential role in the oxidation 

 reactions associated with cell respiration and is therefore necessary for the main- 

 tenance of health, efficiency, vigor, and resistance. 



Niacin (vitamin P-P. nicotinic acid, the antipeilagra vitamin, GJIsC^N) is a 

 white crystalline substance chemically related to nicotine but with none of the 

 toxicity of the latter. It occurs in association with riboflavin, and is furnished by 

 the same foods. As in the case of other vitamins, niacin is a constituent of respira- 

 tory coenzymes, and probably plays a role in the maintenance of normal tissue 

 metabolism. 



The most important therapeutic use of niacin is in the prevention and cure 

 of the serious nutritional disease known as pellagra, which involves the digestive 

 tract, the skin, and the nervous system, with severe mental symptoms in the 

 later stages and often death as the result. This disease is commonly associated 

 with diets rich in corn (maize), and this has led to the discovery that it is de- 

 ficiency of the amino acid tryptophan in corn that is responsible. Tryptophan 

 seems to be the immediate precursor from which niacin is manufactured in the 

 tissues; a corn diet therefore produces niacin deficiency. Administration of the 

 vitamin causes immediate improvement and ultimate complete recovery unless 

 degenerative changes have occurred. 



The folic acids. These are a large and still imperfectly understood group of 

 B-complex vitamins, some of which have already been shown to be necessary in 

 human nutrition. The folic acids are present in many foods, some of the best 

 sources being kidney, liver, mushrooms, yeast, and green leafy vegetables. In 

 rats synthesis of these vitamins by intestinal bacteria is so effective that de- 

 ficiencies can be produced only by reducing the bacterial population of the 

 intestines by means of sulpha drugs. In monkeys and man there seems to be less 

 intestinal synthesis. The blood condition in man called macrocytic anemia is 

 prevented and cured by the folic acids known as PGA, P3GA, and P7GA. This 

 condition is found in sprue and some other diseases and consists of a marked 

 reduction in number and increase in size and hemoglobin content of the red blood 

 cells. Pernicious anemia patients are benefited but not cured by these folic acids. 

 The curative property of liver extract in pernicious anemia is now thought to be 

 due to another member of the B complex, B i2 (animal protein factor), mentioned 

 below. 



Ascorbic acid (vitamin C, the antiscorbutic vitamin, C 6 H 8 06) is one of the 

 longest known vitamins and the only one of the three originally recognized that 

 has not been subdivided. It occurs in fresh fruit and fresh meat and can be syn- 

 thesized by many animals but not by man, monkey, and guinea pig. Since it is 

 very largely destroyed or lost by cooking, raw fruits or vegetables are required 

 as a part of human diet. 



Vitamin C affects the health of all the tissues of the body, but the details of its 

 functioning are not understood. It seems to be necessary for the formation of the 



