160 Messrs. H. G. Thornton and G. Smith. 



that the strong growth of the Euglena might be connected with the slight 

 bacterial growth. 



To test this hypothesis, lesser amounts of alanine and glycocoll were added 

 to the Miquel mixture. 



From 0*2 c.c. to - 5 c.c. were added to 10 c.c. of the optimal Miquel 

 mixture. In cultures started from a ring of encysted forms it was found 

 possible to obtain extremely good growths of Euglena by this means, the 

 bacterial growth being very much lessened. 



It is thus obvious that the Euglena can use alanine and glycocoll, as well 

 as tyrosin and phenylalanine, provided its growth is not inhibited by the 

 rapid development of bacteria, such as always takes place in the glycocoll 

 and alanine solutions when they are too strong. This result is of importance 

 as indicating that the amido-acids are used as such by the Euglena, and not 

 after being decomposed by bacterial growth. Thus, attempts made to grow 

 Euglena in tubes containing an alanine medium in which bacterial decom- 

 position had proceeded for a long time were entirely unsuccessful. 



It is interesting to notice in this connection the fact mentioned above that, 

 in the case of tyrosin, the addition of the solid substance to the tubes causes 

 a considerable bacterial growth, which, after about three weeks, was sufficient 

 to inhibit the proper growth of the Euglena. ISTencki* has shown that, 

 under the influence of anaerobic bacteria, tyrosin is converted into oxyphenyl- 

 propionic acid, 



OH A 



\J CH 2 .CH 2 .COOH, 



and it is probable that, under the aerobic conditions met with in the culture 

 tubes, further decomposition into oxyphenylacetic acid and phenol takes 

 place. 



Decomposition along similar lines occurs when phenylalanine is subjected 

 to bacterial growth, phenylpropionic acid and phenylacetic acid being 

 formed. Thus, when tyrosin and phenylalanine are added in the solid 

 condition, their solutions are sufficiently strong to allow a growth of 

 bacteria, which decompose them into phenol derivatives that are harmful to 

 the Euglena growth. 



We may suppose that, in the same way, harmful products are produced 

 by bacterial action on alanine and glycocoll, so that the Euglena is prevented 

 from developing in the solutions of a strength adapted to the growth of 

 bacteria. 



Other nitrogenous compounds have been tried, e.g. urea, uric acid, and 

 * Nencki, 'Ber. d. Deutsch. Chem. Gesellsch.,' 1874, p. 1593. 



