ON THE FEEDING HABITS OF AMEBA 575 



several times in succession, but with each eating the grain be- 

 comes less attractive, until finally it is refused. If a new grain 

 is then presented it is usually eaten. 



8. The ameba can sense carmine grains twenty microns in 

 diameter at a distance of at least 100 microns, and if the ameba 

 reacts positively at all, it goes unerringly toward the carmine 

 grain. 



9. A few minutes after the carmine is eaten the ameba changes 

 its direction of movement in such a way as to get rid of the car- 

 mine as soon as possible. The new direction of movement, if 

 not a complete reversal, is a resultant of the tendency to move in 

 the original direction and the tendency to move away so that the 

 carmine shall at once come to lie in the new posterior end. 



10. The ectoplasm (of the granular amebas) finds the carmine 

 attractive, the endoplasm repulsive; that is, ectoplasm and endo- 

 plasm react to carmine in opposite ways. 



11. Ameba reacts to india ink in essentially the same way as 

 to carmine, but india ink is less attractive than carmine. 



12. Uric acid grains are eaten less readily than carmine. 



13. Solid egg white that is almost insoluble is eaten much less 

 readily than carmine. Only very hungry amebas eat solid egg 

 white. Amebas in a condition of mild hunger usually react 

 negatively to this substance. Solid egg white, as well as uric 

 acid, india ink, and carmine, is sensed at a distance. 



BIBLIOGRAPHY 



Duncan, P. M. 1877 Studies amongst Amoebae. Pop. Sci. Rev., vol. 16, pp. 



217-234. 45 figures. 

 GiBBS, D. and Bellinger, O. P. 1908 The daily life of Amoeba proteus. 



Amer. Jour. Psychol., vol. 19, pp. 230-241. 7 figures. 3 plates. 

 Harrington, N. R. and Leaming, E. 1900 The reaction of Amoeba to light of 



different colors. Amer. Jour. Physiol., vol. 3, pp. 9-18. 2 figures. 

 Jennings, H. S. 1904 Contributions to the study of the behavior of the lower 



organisms. Carnegie Inst. Pub., no. 16, pp. 256. 81 figures. 

 Kepner, W. a., Taliaferro, W. H., et al., 1913 Reactions of Amoeba proteus 



to food. Biol. Bull., vol. 24, pp. 411-428. 3 plates. 1 figure. 

 Leidy, J. 1879 Freshwater Rhizopods of North Ajnerica. Report U. S. Geol. 



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