60 orr.M rn .. h i:in:niTy a\d I':\] ihoxmext 



mine the sign of asymmetry of protoplasm, wliicli is, 

 according- to all evidence, the result of a long evolution- 

 ary development. 



Among more recent investigations on the inefficacy of 

 culture media on the sign of optical activity of primary 

 constituents of protoplasm, we shall mention those of 

 Gause and Smaragdova (1938). These authors have 

 studied the etfect on the yeast, Torula iitilis, of a pro- 

 longed cultivation in the optical isomers of leucine. The 

 yeast was cultivated at 27° C on pure left leucine in one 

 series and on pure right leucine in another. During the 

 iy2 months that the experiment lasted, 14 passages were 

 made. At the end of this period the rate of growth in 

 both series was measured. A similar procedure was fol- 

 lowed for a study of the action of right and left valine. 

 It was found that, though growth of Torula proceeds 

 much more rapidly on the biological forms of these amino- 

 acids (laevorotatory leucine and dextrorotatory valine), 

 there is some growth on their optical antipodes. It should 

 be noticed that the majority of other yeasts cannot grow 

 at all on the unnatural isomers of amino-acids. The very 

 possibility of a weak but unlimited growth of Torula 

 utUis on the right leucine and on the left valine is corre- 

 lated with the fact that these substances are first deamin- 

 ated by yeast (leucine, according to Ehrlich, 1906, is 

 transformed into iso-amyl alcohol), and the ammonia 

 thus formed proves to be a sufficient source of nitrogen 

 for the unlimited growth in Torula utilis. But the supply 

 of nitrogen in the form of ammonia alone is not sufficient 

 for most of the otljer species of yeast and a prolonged 

 growth on the unnatural isomers of amino-acids cannot 

 take place in them. 



As was to be expected, a prolonged cultivation of Torula 

 on such nonbiological isomers had no essential influence 

 on the asymmetric properties of the protoplasm of these 

 yeasts, so that growth always remained more rapid on the 

 natural amino acids. Structurally inappropriate isomers 



