474 ME. HAEOLD WAGEE ON THE 



50 per cent, solution o£ alcohol. Dilute glyceriue is the best 

 mounting medium, but fairly satisfactory preparations may be 

 made either in glycerine- jelly or Canada balsm. 



In good preparations the contents of the cell appear black, the 

 eye-spot black and sharply defined, and the flagellum with its 

 enlargement dark grey. 



I have occasionally succeeded in staining the flagellum and 

 enlargement light green in a mixture of methyl-green and 

 fuchsin. Pig. 2 is from a preparation made in this way and 

 mounted in dilute glycerine. 



The Effect of Light on Euglena. 



In common with many other unicellular motile organisms 

 which contain chlorophyll, Euglena is extremely sensitive to 

 light. Our knowledge of the phenomena is mainly due to 

 the investigations of Stahl *, Strasburger t, and Engelmann %. 

 They find that in general the cells are attracted by a light of 

 moderate intensity and repelled by an intense light ; but that 

 the degree of sensitiveness which they exhibit varies considerably 

 even in individuals of the same species. Further, both Klebs 

 and Strasburger have shown that they do not lose their sensi- 

 tiveness to light either in the dark or at a higher temperature; 

 and Englemann has also shown that this power is independent 

 to a high degree of a variation in the oxygen pressure. 



The effects produced by the action of light upon the motile 

 cells of Euglena are very striking. They are strongly attracted 

 by a bright light such as that of a gas-flame or incandescent 

 burner focussed, by means of a substage condenser, upon a 

 microscope-slide on which a drop of water containing Euglence 

 has been placed. Such a spot of light will attract, in the space 

 of about one minute, the majority of the cells in the field of the 

 microscope, as seen by a one-inch objective ; and in two minutes 

 only very few will be found outside the light area. If a large 

 number of cells are present, they will form a seething mass in 



* " Ueber den Einfluss von Richtung und Starke der Beleiichtuug auf einige 

 Bewegungserscheinungen im Pflanzenreiche." Bot. Zeitung, 1883. 



t " Wirkimg des Lichtes und der Warme auf Schwarmsporen." Jena. 

 Zeitschr. xii., 1878. 



J " Ueber Licht und Farbenperception niederster Organismen." Pfliiger's 

 Archiv, Bd. 29, 1882 (see J. E. M. S. 1883, p. 81). 



