438 VITAMIN Bi2 



by vitamin B12 or folic acid. There was no growth response to homocystine 

 unless vitamin B12 was also added; the responses to mixtures of homo- 

 cystine and betaine or homocystine and choline in the absence of vitamin 

 B12 was no greater than the responses to betaine or choline when added 

 singly. However, when vitamin B12 was supplied, there was a response to 

 homocystine. The growth-promoting effect of folic acid was markedly af- 



TABLE VI 

 Weights of Chicks at 25 Days on Purified Diet 1 (Glucose + 25% Soybean 

 Protein) with Various Supplements 



fected by the other supplements; a sparing action of folic acid on the 

 requirement for choline is illustrated by the following data: 



Additions Weight at 25 days 



Vitamin B12 182 



Vitamin B12 + folic acid 225 



Vitamin B12 + choline 233 



Vitamin B12 + folic acid + choline 255 



Vitamin B12 + homocystine 242 



Vitamin B12 + homocystine + folic acid 321 



Vitamin B12 + homocystine + choline 325 



Vitamin B12 -|- homocystine + folic acid + choline 324 



These data can be explained by assuming that folic acid in the presence of 

 vitamin B12 is needed for the methylation of dimethylaminoethanol to 

 form choline. When preformed choline was supplied, the requirement for 

 folic acid for this purpose disappeared. 



Using diet 2 which contained added folic acid but not dimethylaminoeth- 

 anol, it was again found that no response was produced by homocystine 

 unless vitamin B12 was added, but methionine produced responses regard- 

 less of the presence or absence of vitamin B12. The results are shown in 

 Tables VII and VIII. The leg-bone deformity termed "porosis" was ag- 

 gravated by vitamin B12 in the absence of choline, confirming an earlier 

 observation.^"^ When diet 3, which was more deficient in methionine than 

 diets 1 and 2, was used, the effect of vitamin lin on the utilization of 

 homocystine was even more marked and is illustrated in Fig. 5. If, however, 



