240 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



For various reasons a number of the water-soluble vitamins have 

 been grouped together as the vitamin-B complex. Vitamin Bi and 

 vitamin G were the orginal members of this group which now in- 

 cludes nicotinic acid and vitamin Be as well as five or six other 

 factors not mentioned in this discussion. 



The number of vitamins actually known to be essential in human 

 nutrition is relatively small. The importance of vitamins A, Bi, and 

 C in the diet is now well known. It is certain that vitamin D is a 

 requirement of children, and while it may be needed by adults as 

 well, perhaps in lesser amounts, this is yet to be demonstrate^. Evi- 

 dence of the significance of riboflavin (vitamin G) in the Hiet of 

 man has been obtained within the last 2 years, and we now have a 

 clear picture of the external symptoms that follow the use of a diet 

 deficient in this factor. Since the announcement in 1937 of the value 

 of nicotinic acid in the cure of the disease in animals which is com- 

 parable to pellagra in man, considerable information has accumu- 

 lated to establish the value of this substance as a pellagra preventive. 

 There is still some question as to whether nicotinic acid and/or 

 nicotinamide can unreservedly be designated the pellagra-preventing 

 or P-P factor or factors, but there can be no doubt that they are 

 specific in their effect on certain symptoms of pellagra. The sub- 

 stance in foods which is referred to as vitamin K helps promote the 

 clotting of blood, and the supposition now is that it functions in 

 man, as well as in animals, in maintaining a normal level of pro- 

 thrombin in the blood. An anemia which occurs in chicks given a 

 diet deficient in vitamin K responds to treatment with extracts 

 containing this vitamin. 



These are the vitamins definitely known to be required by man. 

 There is also considerable evidence in favor of two others, vitamin 

 E and vitamin Be. Vitamin E (alpha-tocopherol) has been shown to 

 be important for normal reproduction in several species of animals 

 and it may be required for successful reproduction in the human 

 species as well. Both vitamin E and vitamin Be are being actively 

 investigated at the present time. 



The importance of the vitamins to normal nutrition is now fully 

 recognized, although there is still a great deal to learn about these 

 substances. In planning foods for the day it is essential to know 

 how to select them for vitamin values as well as for their content of 

 protein, carbohydrate, fat, and minerals. The purpose of this article 

 is to give a brief and not too technical presentation of our knowledge 

 of the properties and food sources of these vitamins. A brief de- 

 scription of the method of quantitative expression used for them and 

 a table of values for vitamin A, vitamin Bi, vitamin C, and riboflavin 

 content of common foods are also included. 



