VITAMINS 249 



In all of the above diseases the administration of relatively large daily- 

 doses (about 4 g.) of a simple pyrimidine compound, namely thymine 

 (p. 155), has an almost equally beneficial result. From this and other 

 evidence it seems probable that the biological function of pteroylglutamic 

 acid is concerned with the biosynthesis of thymine and other components 

 of nucleic acids. Teropterin has been claimed to relieve pain in advanced 

 cases of human cancer and to retard the growth of tumors in experimental 

 animals., '„€) 



Ir 



Food sources and requirements fe^nl^, 



The pteroylglutamic acids are rather sensitive substances which may 

 be quite largely destroyed during the cooking of foods. Losses of 50 

 to 90 per cent have been reported in meats cooked in different ways. 

 Vegetables kept for three days at room temperature lost 20 to 80 per 

 cent, and large losses occurred during canning. When a solution of the 

 pure vitamin was placed in bright daylight for 8 hours, 88 per cent was 

 destroyed. 'i^^ t> 



.^According to Toepfer ^H co-workers a number of common foods may 

 be^rouped as follows, oA4he basis of the milligrams of folic acid which 

 they contain per 100 g. of dry weight: Over 1,0:^. brewer's yeast, chicken 

 liver, _^sparagus, broadleaf endive, broccoJi, l^^'lettuce, spinach; 0.4-1.0, 

 most of the other leafy greens, liver, blackey'e peas, dried beans, soy 

 flour; O.l-d.4, other vegetables except root vegetables and a few fruits; 

 0.03-0.1, root vegetables, most fresh fruits, grains and grain products, 

 nuts, lean beef; 0.03 or less, eggs, milk, meats (other than beef), poultry. 



The amount of pteroylglutamic acid normally required by human 

 beings has not been established. Various animal species need 0.005 to 

 0.06 mg. per kilogram of body weight per day. 



VITAMIN B^o 



It has long been recognized that liver and suitable extracts prepared 

 from liver contain some substance which is effective in the treatment 

 of pernicious anemia, a serious, wasting disease of man, which if untreated 

 is invariably fatal. IMany efforts to isolate and identify the "antiper- 

 nicious anemia factor" in liver have been made. With the discovery 

 of pteroylglutamic acid and the observation that it is effective in curing 

 certain pathological blood conditions, it seemed that the long-sought 

 substance might have been found. However, continued treatment of per- 

 nicious anemia patients with pteroylglutamic acid proved disappointing, 

 since the initial improvement did not last and was often followed by 

 severe neurological complications. 



Finally, in 1948, a red crystalline substance was isolated from liver 



