256 VITAMINS 



Deficiencies of pantothenic acid, para-aminobenzoic acid, copper, and 

 biotin have each been reported to cause such graying. However, there 

 is at the present time no acceptable scientific evidence that gray hair in 

 human beings can be restored to its original color by the dietary use 

 of any of these materials, or of any other "gray hair factor." 



Other less well-defined factors are vitamin P, which has been reported 

 to correct bleeding caused by weakened capillaries in human beings, 

 vitamin B13, and vitamin B14. A large number of other vitamin-like sub- 

 stances are apparently needed for the normal nutrition of various species 

 of animals, and particularly of microorganisms, but knowledge of their 

 nature and biologica'l significance is too limited to warrant their con- 

 sideration here. 



Antivitamins 



Substances chemically related to certain vitamins interfere with their 

 normal physiological functioning and are therefore called antivitamins. 

 For example, mice fed pyrithiamine (a thiamine analog, see formula) 

 develop typical symptoms of thiamine deficiency. Similarly, pyridine-3- 



CH3 CH2CH2OH 

 N=C— NH2 C— C^ 



II / w 



CH3— C C— CH2— N CH 



II II "V / 



, Pyrithiamine 



sulfonic acid and glucoafecorbic acid act as antagonists of nicotinic acid 

 and vitamin C, respectively. In each case, administration of the vitamin 

 concerned corrects the deficiency, and it appears that the response of 

 the organism depends on the relative amount of the vitamin and anti- 

 vitamin present. 



An explanation for behavior of this sort was advanced by Woods and 

 Fildes who found that p-aminobenzoic acid (PABA) can counteract the 

 antibacterial effect of the drug, sulfanilamide. They suggested that 

 PABA is an essential metabolite for the bacteria and that sulfanilamide 

 exerts its effect by acting as an inhibitor of the bacterial enzymes con- 

 cerned with the metabolic use or functions of PABA (e.g., conversion to 



COOH SO2NH2 



C C 



p-Aminobenzoic acid Sulfanilamide 



