REACTIONS OF AMEBA TO LIGHT, 71 



with the beam it either flows over it indifferently, or it reacts 

 negatively to the beam by changing its direction of movement. 



2. Beams of spectral light and of white light have approxi- 

 mately the same general effect. It appears however that spectral 

 light at the blue end is somewhat less attractive than that at the 

 red end. 



3. Beams of darkness are also sensed at a distance like beams 

 of light. They are usually negative. That is, the ameba usually 

 avoids the beams before coming very near them. 



4. It is the change of light intensity that determines changes 

 in reactions. Neither high nor low intensities seem to be either 

 negative or positive in themselves. Movement from a region 

 of low light intensity into a region of high intensity frequently 

 occurs if the contrast is not too great; but movement toward a 

 region of lower light intensity (dark beams) is seldom seen. 



5. No explanation is suggested for the sensing of beams of 

 light and of darkness at a distance. The nature of the stimulus 

 and the means of its transfer in such cases is not known. 



6. Grains of globulin illuminated by perpendicular beams of 

 light seem, on the whole, to be at least as attractive as when not 

 more brightly illuminated than the field. But when globulin 

 grains are laid in large dark beams, the ameba frequently shows 

 unmistakable signs of a tendency to react negatively. 



7. Both light beams and globulin grains are positive when 

 stimulating the ameba separately; but when a grain of globulin 

 and a beam of light, placed a small distance apart from each 

 other, stimulate the ameba simultaneously, the more weakly 

 positive object the beam of light becomes usually strikingly 

 negative. 



8. An ameba is positive, negative or indifferent to beams of 

 light depending upon circumstances. 



BIBLIOGRAPHY. 

 Davenport, C. B. 



'97 Experimental Morphology. New York. Vol. I, pp. 280. 

 Harrington, N. R. and Learning, E. 



'oo The Reaction of Amoeba to Light of Different Colors. Amer. Jour. 



Physiol., Vol. 3, pp. 9-18. 2 figs. 

 Mast, S. O. 



'10 Reactions to Light in Amoeba. Jour. Exp. Zool., Vol. 9, pp. 265-277. 2 

 figs. 



