On the Growth of certain Fresh-water arid Soil Protista. 159 



with a ring of encysted forms, as described above, produced a considerable 

 growth. 



The great superiority of the tyrosin solutions over the solutions of 

 glycocoll and alanine was very marked. It was at first thought possible 

 that this was due to the presence of the benzene ring in the tyrosin, 

 especially since alanine is similar in composition to tyrosin, except that in 

 the former substance the oxyphenyl ring is absent. 



OH A 



CH 3 .CH(NH 2 ).COOH. \/ CH 2 .CH(NH 2 ).COOH. 



Alanine. Tyrosin. 

 With a view to testing this hypothesis, the phenyl compounds of alanine 

 and glycocoll were employed in the culture media. 

 In media containing phenyl glycocoll, 



/\ 



CH(NH 2 ).COOH, 



it was found that no growth took place, even the development of the 

 bacteria being prevented. 



But, in the media containing phenylalanine, 



/\ 



\J CH 2 .CH(NH 2 ).COOH. 



a very strong growth of Euglena was produced, bacterial growth being at 

 first slight, but increasing after some time. Since this compound resembles 

 tyrosin in being very insoluble, it was added to the media in a solid form. 

 Attempts to grow Euglena in saccharin, 



S0 2 



co >NH - 



showed that this substance prohibited all growth of the organism. 



The negative results obtained with phenyl glycocoll and with saccharin 

 showed that, at any rate, the mere presence of the benzene ring was not the 

 essential factor for the growth of the Euglena. 



Since the substances that are most successful for the propagation of 

 Euglena, namely, tyrosin and phenylalanine, are only very slightly soluble, 

 so that exceedingly weak solutions are used, and since, on this account, 

 bacterial growth in these solutions is very slight compared with that which 

 occurs in the stronger solutions of alanine and glycin, it seemed possible 



