152 Messrs. H. G. Thornton and G. Smith. 



chemically pure organic compounds instead of the indefinite composition of 

 an organic infusion. 



The method employed in the cultures of Euglena viridis has also been used 

 to study the minute bacterial feeding flagellates living in the soil. 



Experiments with Euglena viridis. 



In culture experiments with Euglena gracilis, Zumstein* found that a 

 much improved growth could be obtained if a little organic matter was 

 added to the culture medium. By increasing the amount of organic matter 

 in the medium, he found that Euglena gracilis could be induced to change 

 its mode of nutrition, living solely as a saprophyte. Under these conditions 

 the Euglena passed into an Astasia-like form, the chlorophyll disappearing 

 and leaving only the colourless leucoplasts. When living saprophytically, 

 the organism could thrive in the dark as well as in the light. Zumstein 

 found that the green coloration was reassumed if the Astasia form was 

 brought back into a solution containing only a small amount of organic 

 matter and kept in the light. 



Trebouxf was able to grow Euglena gracilis in solutions containing citric 

 acid, but found that Euglena viridis could not be grown under these 

 conditions. Thus, there appears to be a marked physiological difference 

 between these two species of Euglena, a fact which is emphasised by the 

 earlier work of Klawkine| on Euglena viridis. His experiments showed 

 that it was impossible to make Euglena viridis thrive well in the dark. 

 When kept in the dark in a medium containing organic matter, the 

 Euglenas remained alive, but did not lose their chlorophyll or show a 

 perceptible increase. Our experiments with this species of Euglena have 

 confirmed the results obtained by Klawkine, and show that Euglena viridis 

 is not able to thrive in the absence of light, even when placed in. the 

 optimal culture medium and in the presence of suitable organic matter. 



It is thus evident that Euglena viridis is a more essentially holophytic 

 organism than Euglena gracilis, a fact which tendp to simplify the issue when 

 we come to study the physiology of its nutrition. 



By appropriate methods, a culture of Euglena viridis has been kept in 

 active growth in test-tubes by inoculation from tube to tube, for a period of 

 about two years. 



* H. Zumstein, " Morphologie und Physiologie der Euglena gracilis," ' Pringsheim's 

 Jahrbucher f. wiss. Botanik,' vol. 34, p. 419 (1899). 



+ 0. Treboux, "Organische Sauren'als Kohlenstoffquelle bei Algen," 'Ber. d. D. B. 

 Ges.,' vol. 23, p. 432 (1905). 



\ W. Klawkine, " Becherches biologiques sur V Astasia ocellata et V Euglena viridis," 

 ' Ann. des Sci. Nat., Zool.,' serie 6, vol. 19, and serie 7, vol. 1. 



