186 LIGHT AND PROTOPLASM [Ch. VII 



impinging rays of light, hy means of a Mack cardboard hex placed over the slide. 

 Thus it is clear that all of his light fell upon the organism in perpendicular 

 rays from below. This method of experimentation would clearly not show 

 ■whether Amoeba is phototactic or not. 



I have experimented with Amoeba proteus, using methods 

 resembling Verworn's, and likewise dissimilar ones, and have 

 reached new results. In the first place, I have proceeded some- 

 what after the fashion of Vbrworn to determine whether the 

 amoeba in a field illuminated from below, and separated by a 

 sharp line into a light and dark half, showed any change of 

 movement in passing from dark to light or from light to dark ; 

 also, whether an amoeba moving in a uniformly illuminated 

 field changed its direction when half of its body was dark- 

 ened. Nearly all such experiments were negative. No effect 

 resulting from the change from light to dark or the reverse 

 could be detected. Thus far my results agreed with Ver- 

 worn's. 



In a second set of experiments, I proceeded differently. 

 Usually one amoeba was isolated by means of a capillary tube. 

 It was then introduced, with a drop of clear water, between 

 two slips of glass, each about 25 by 50 mm., which were kept 

 2 mm. apart, and at the same time cemented together, by glass 

 strips of equal thickness placed near the ends. By this means a 

 broad field for movement with uniformity of conditions of con- 

 tact was ensured. The whole space between the two glass plates 

 being now filled with clear water, the entire apparatus was sub- 

 merged in a vessel which contained water about 2 cm. deep, 

 and which was slightly smaller than the stage of the micro- 

 scope. Finally, the entire stage, but not the substage optical 

 apparatus, Avas kept in the dark by means of a cone made of 

 several thicknesses of dense black cloth fastened by a slip-noose 

 to the objective, and folded below the stage so as completely to 

 exclude all extraneous lateral light. Light from the mirror 

 was cut off by an interposed card. Through a slit in the cloth 

 on the side next the window, — a west window, — a beam of 

 direct sunlight, or of reflected light from the morning sky, was 

 admitted to the amoeba. The plates of glass being as nearly as 

 possible horizontal and occasionally rotated, the directive action 

 of gravity was eliminated. Since, so far as could be seen with 



