156 Messrs. H. G. Thornton and G. Smith. 



1. Dextrose — 



In media, in which - 5-l c.c. of a 1-per-cent. solution of dextrose was 

 added to 10 c.c. of the " optimal Miquel " solution, no growth of Euglena 

 was observed, but in all cases there was a considerable growth of fungus, 

 probably derived from spores from the stock tube of Euglena. It is probable 

 that the great development of the fungus inhibited the growth of the 

 Euglena, since a slight growth in the optimal Miquel solution was expected. 



2. Cane Sugar — 



The addition of Oo-l c.c. of a 1-per-cent. solution of this substance to 

 10 c.c. of the " optimal Miquel " solution did not inhibit the growth of the 

 Euglena to the same extent as the dextrose, but only rarely and after a long 

 period did any noticeable growth appear. The growth of fungus in these 

 tubes was either absent or very slight. 



3. Tartaric Acid — 



The addition of 1 c.c. of a 1-per-cent. solution bad a purely negative 

 effect, no growth of Euglena but a strong growth of fungus being observed. 



It is evident from these results that the stimulating element in the 

 organic infusion is not in the nature of a carbohydrate. 



4. Peptone — 



The addition of 1 c.c. of a 1-per-cent. solution of peptone to the medium 

 invariably gave rise to a very strong bacterial growth, the bacteria being no 

 doubt introduced with the Euglena, on inoculation. Under these conditions 

 the Euglena scarcely developed at all, although it is not entirely killed off, 

 a slight ring appearing at the top of the fluid. 



5. Amido-acids* — 



Tyrosin. — As this compound is very insoluble in water, a saturated 

 solution was made up in distilled water. The saturated solution when cold 

 contains the salt in the proportion of 1 in 2400 of water. 



In the earlier experiments 1 or 2 c.c. of the above solution were added to 

 10 c.c. of the "optimal Miquel" mixture. A very strong growth was 

 obtained in this medium, indeed superior to that obtained by means of the 

 addition of a natural organic infusion. The marked difference in the growth 

 of the Euglena in a tube containing this minute trace of tyrosin (1 : 24,000) 

 as compared with a culture in a medium free from organic matter, may be 

 seen in the photograph (fig. 1). 



* A number of experiments have been made by Loew, Bokorny, and others on the 

 growth of algae in amido and fatty acids. A full literature of this work will be found 

 in Oswald Bichter's 'Die Ernahrung der Algen,' 1911. 



