52 E. J. LUND 



8. Rise in temperature increases the rate of feeding on yolk. 



9. Continuous action of white Ught of high intensity had no 

 detectable effect upon feeding on yolk. 



10. Feeding may continue during stimulation by a direct elec- 

 tric current of sufficient intensity to control the direction of 

 movement of the organism. 



11. Bursaria can discriminate between and select non-toxic 

 grains of yolk from among toxic ones. Whether or not Bursaria 

 will eat yolk grains that have adsorbed a soluble substance de- 

 pends upon (a) the steepness of the effective concentration gra- 

 dient of the dye, between the grain and the non-toxic medium; 

 and this in turn depends upon the amount of dye adsorbed 

 which is subject to a reversible adsorption; (b) the specific chem- 

 ical properties ('taste'?) of the substance adsorbed. 



12. There are strong reasons for believing that different parts 

 of the cell are affected unequally by certain toxic substances, and 

 that these may have a specific action upon the selection mecha- 

 nism, causing a more definite rejecting reaction. 



13. Yolk which has adsorbed a substance which is insoluble 

 in water (Sudan III) is eaten as readily as fresh unstained yolk. 



14. Bursaria has the power of selective extrusion among vacu- 

 oles each containing different substances eaten at the same time; 

 vacuoles containing indigestible substances are soon extruded, 

 while those containing food are retained. If fat-free yolk is 

 present in the same vacuole along with the indigestible sub- 

 stance, then the latter is retained until digestion of the enclosed 

 yolk has run its usual course. 



LITERATURE CITED 



Greenwood, M. 1894 On the constitution and mode of formation of food 



vacuoles in Infusoria, etc. Philos. Transact. Roy. Soc, London, vol. 



1S.5, B, p. 355. 

 Metalnikow, S. 1912 Contributions a I'etude de la digestion intracellulaire 



chez les Protozoaires. Arch. Zool. Exper., tome 9, pp. 373-499. 

 ScHAEFFER, AsA ARTHUR 1910 Selection of food in Stentor coeruleus (Ehr.) 



Jour. Exper. Zool., vol. 8, pp. 75-132. 



