222 PHYSIOLOGICAL CHEMISTRY 



hitherto undreamed of, are absolutely essential to the health and 

 even the life of the individual. The chemical nature of these 

 substances is still unknown, but it appears that there probably 

 are at least four and possibly more of them. 



The discovery of the existence of these substances was inti- 

 mately connected with a disease known as beri-beri prevalent in 

 oriental countries where the natives live on a diet consisting 

 mainly of polished rice. On such a diet, extensive disturbances 

 of the nervous system develop, resulting in weakness, paralysis 

 and ultimate death. Feeding the outside layer of rice, ordi- 

 narily removed in polishing, causes immediate relief and speedy 

 recovery. A substance evidently is present in the outer layer 

 of rice, without which an animal on a polished rice diet devel- 

 ops beri-beri. Later work has shown the substance to be present 

 mainly in the embryo. A similar condition appears in chickens 

 on a rice diet, and extensive studies have been carried out to 

 ascertain the nature of the curative substance and of the disease. 

 Funk has called the unknown material "vitamine," a name to 

 which there are some objections, and believes that the substance 

 contains nitrogen. 



The investigation of these unknown, but essential dietary 

 constituents is made difficult by the fact that they are present 

 in the foods and are required by the body in extremely minute 

 amounts, a few milligrams being sufficient to supply all the 

 body's daily needs. 



Just why the body needs these materials and the functions 

 which they perform are matters as yet obscure. Possibly they 

 stimulate or regulate the functioning of certain tissues or cells, 

 possibly they are used as materials for the construction of cer- 

 tain products of internal secretion which are required in the 

 processes of metabolism. The riddle is still unsolved, but never- 

 theless, we are closer to its solution than were our ancestors, 

 who did not dream of the existence of these vitally important 

 compounds. 



Since the earlier observations were made, much interest has 

 centered on diseases which appear to be brought about by 



