CHOICE OF FOOD IN AMEBA 251 



indicate, in conformity with the results recorded in my previous 

 papers, that some physical disturbance propagated radially from 

 the source of stimulation is an essential factor in determining 

 the direction of movement of the ameba. 



3. No definite statement can be made regarding the basis 

 upon which choice in general is made. In a general way only 

 digestible substances are eaten, but some digestible substances 

 are refused (zein, gelatin) and some indigestible substances 

 (carmine, india ink) are readily eaten. It can be stated however , 

 that the basis of selection is not chemical in any known case 

 and that in several important cases selection is based upon 

 physical properties. 



4. Movement of a particle is one of the most important, if 

 not the most important food quality a particle can possess. 

 Particles of glass, which are never eaten when lying still, are 

 readily eaten when agitated. 



5. The experiments with mechanically agitated particles bring 

 out very strikingly the difference between organismal and histonic 

 selection. The ingesting and the digesting mechanisms differ 

 profoundly as to the food value of a particle of agitated glass, 

 for example. 



6. Observation and experiment indicate that amebas might 

 possibly be able to exist and propagate indefinitely in nature 

 if they selected their food on the basis of movement alone. • 



7. The experiments show that, in many cases, past experience 

 in receiving stimuli or in feeding is of more importance in 

 selection than the nature of the stimuli received from a present 

 object. 



Many individual acts of selection cannot therefore be explained 

 when standing alone, but only when the ameba's past, especially 

 its immediate past, is known. Selection is therefore a historical 

 process. The main factors, then, that enter into selection are 

 physical and experiential. 



BIBLIOGRAPHY 



Gibbs, D. and Dellinger, A. P. The daily life of Amoeba proteus. Amer. 



1908. Jour. Psychol., vol. 19, pp. 230-241, 7 figs., 3 plates. 

 Lund, E. J. The relations of bursaria to food. Jour. Exp. ZooL, vol. 16, pp. 



1914. 1-52, 8 figs. 

 Metalnikow, S. Contributions a l'etude de la digestion intracellulaire chez les 



1912. protozoaires. Arch, de Zool. Exp. et Gen., (5 e Serie, T. IX) vol. 

 XLIX, pp. 373-498, 3 figs., 2 plates. 



