236 



VITAMINS 



of the skin, particularly on the hands, arms, face, and back of the neck. 

 Apparently the sun exerts an irritating effect, causing exposed areas of 

 the skin to exhibit first this abnormality. The mouth becomes sore be- 

 cause of lesions which develop on the mucous membrane, and the tongue 

 may become sore, red, and swollen. Indigestion and diarrhea are asso- 

 ciated conditions, and in severe cases insanity may result. The symptoms 

 of pellagra have been summed up by the "three D's": dermatitis, diar- 



Courtesy of J. M. Ruffln, D. T. Smith, and The Southern Medical Journal. 

 Fig. 9-9. Effect of nicotinic acid on dermatitis of pellagra. 



rhea, and dementia. In dogs the disease is known as black-tongue. Pigs 

 and monkeys have also been shown to develop a similar disease when 

 deprived of nicotinic acid. Rats, on the other hand, apparently do not 

 require this vitamin in the diet. 



Nicotinic acid, like riboflavin, is an essential constituent of several en- 

 zyme systems. In fact, it is a definite part of triphosphopyridine nucleo- 

 tide (TPN, p. 275) , without which one cytochrome reductase cannot func- 

 tion. In addition to the amide of nicotinic acid this coenzyme contains 

 adenine, two molecules of ribose, and three molecules of phosphoric acid. 

 A compound differing from this only in that it contains one less phos- 

 phoric acid molecule is diphosphopyridine nucleotide (DPN), which is 

 essential to the breakdown of glucose by animals and to fermentation 

 by yeast. Its function as a part of oxidation-reduction systems is the 



