92 



.Sl'Ux'AL T]\J,ST AM) OPT. ACTITITY 



These experiments were rei:)eated with the optical 

 isomers of the following- amino acids : leucine, histidine, 

 phenyl-alanine and valine (Gause, 1939). The results 

 obtained are given in Figure 10. Typical heat injury at 

 temperatures extending from 18° to 28° may be observed 

 in the growth of Torula nfills on the unnatural isomers 

 of leucine and of histidine but not on those of valine and 

 phenyl-alanine. 



80- 



60 



40 

 20 



25 



20 



140 iQO 22° 26° 



18° 22° 26°C 



10 

 5 



Fig. 10. Growth of the yeast Torula iitilis on optical isomers of 

 various amino acids, at different temperatures. Abscissae: Temperature 

 in degrees C; Ordinates: Increase in the number of cells in 40 hours. 

 (Prom Gause, 1939.) 



