XI. REQUIREMENTS AND FACTORS INFLUENCING THEM 217 



the sole form of anti-anemia tlierapy. In such cases, th(> neurolojijic damage 

 following its use is probably attnl)Utal)le to extreme depletion of vita- 

 min Brj .^ 



XI. Requirements and Factors Influencing Them 



A. OF ANIMALS 

 (See Section IX.A.) 



B. OF MAN 

 FRANK H. BETHELL 



The daily requirement of PGA for maintenance of normal nutrition is 

 unknown, and data applicable to this problem are difficult to obtain. It 

 would appear, on the basis of food analyses,'-* that the daily dietai-y supply 

 of PGA is probably less than 1 mg. and, owing to losses in cooking, the 

 figure may be only a fraction of a milligram. The accuracy and reliability 

 of food assays for PGA may be impaired by a number of circumstances: 

 (1) Free PGA may not be released from naturally occurring conjugated 

 forms which do not support the growth of the test organisms. (2) Interfering 

 or inhibiting agents may be present. (3) Substances other than PGA which 

 support the growth of the organisms, such as thymine, may be responsible 

 for erroneously high values. (4) Of special importance is the fact that most 

 of the reported food values for PGA were obtained before the existence of 

 the citrovorum factor (CF) was recognized and its microbial growth-stimu- 

 lating properties described. Finally, intestinal bacterial synthesis of PGA 

 or CF Tna.y constitute an important source of the vitamin. 



On the basis of therapeutic experience in PGA deficiency states, it ap- 

 pears probable that the total daily requirement of PGA and its analogs 

 may be supplied by the equivalent of 1 to 2 mg. of the free vitamin. The 

 demand is presumabh' greater in pregnancy, in conditions associated with 

 hypermetabolism, and in disorders characterized by excessive tissue break- 

 down and regeneration. 



'R. W. Viltcr, D. Ilorrigan, J. F. Mueller, T. Jarrold, C. F. Vilter, V. Hawkins, 



and \. Seaman, Blood 5, 695 (1950). 

 ' V. II. Cheldelin. A. M. Woods, and R. J. Williams, J. Nulrition 26, 477 (1943). 

 2 M. Ives, A. E. Pollard, C. A. Elvehjem, and F. M. Strong, /. Nulridon 31, 347 



(1946). 

 5 H. S. Schweigert, A. E. Pollard, and C. A. Elvehjem, Arch. Biochcni. 10, 107 (1946) 

 ' R. II. Girdwood, Edinburgh Med. J. 58, 309 (1951). 



