MONOUNSATURATED FATTY ACIDS 



61 



sence of the fatty acids (0.05 m/^g./tube) restored the growth- 

 promoting potency of the fatty acids. This phenomenon 

 was not observed with the other organisms, but more reliable 

 growth curves were obtained when the media were fortified 

 with 0.01 m/xg. of biotin. 



The growth-promoting activity of c/5-vaccenic, palmito- 

 leic, and d5-7,8-tetradecenoic acid for L. casei and L. 

 delbriieckii is markedly increased by addition of Tween 

 40 to the culture medium. With L. arahinosus, the Tween 

 40 increased the stimulatory effects of c/5-vaccenic and pal- 

 mitoleic acids but suppressed the growth effect of <:/5-7-tetra- 

 decenoic acid. 



The part played by the Tween is obscure but appears to 



0.1 



0.2 



0.3 



0.4 



0.5 



0.6 



Fig. 3.4. Fatty acid growth curves for L. delbrueckii. Abscissa, 

 /iinoles of fatty ,acid per tube. Ordinate, Klett readings. 



