62 Transactions Tennessee Academy of Science. 



the proper sort, it will be eaten, no matter what the composition 

 of the particle is. Now, when it is remembered that ameba, in its 

 natural state, lives practically altogether on living- organisms, it 

 appears that movement in a particle is an adequate stimulus to 

 set off the feeding mechanism ; for movement can be sensed at a 

 distance from the particle, and movement is always associated 

 with a food organism. It may be concluded then that the ameba's 

 chemical sense, if it has any, might atrophy without materially 

 impairing the ameba's effectiveness in feeding. That is, the tact- 

 ual sense is much more important in food discrimination while the 

 ameba is in its natural state than a chemical sense would be. 



This discussion concerning food discrimination refers only to 

 discrimination j^receding the final stage of complete ingestion ; 

 for after ingestion some particles are quickly excreted while oth- 

 ers are kept in the body for a long time. That is to say, there is 

 a form of selection outside the body which differs from that in- 

 side the body ; some substances, such as carmine, are readily in- 

 gested, but usually cjuickly excreted, while other substances, such 

 as grain gluten, which are usually less readily eaten than carmine, 

 are retained for a long time. It is evident, therefore, that dis- 

 crimination can not be made upon the same basis in both cases. 

 To avoid confusion while speaking of food discrimination, it is 

 therefore necessary to keep this distinction in mind. 



T reported at our last meeting that amebas are capable of sens- 

 ing objects at a distance; that they can accurately locate, for ex- 

 ample, a piece of glass at a distance of one-tenth of a millimeter. 

 I have carried out a number of experiments since then that show 

 that vertical beams of white or monochromatic spectral light, one- 

 fiftieth of a millimeter in diameter, can also be sensed at a distance 

 of about one-tenth of a millimeter. The amebas move toward the 

 light beam before they come into actual contact with the beam. 

 (See Fig. 1.) (3ne could, therefore, in the experimental results, 

 change "fragment of glass" for "beam of light", and ficc T'crsa, 

 without necessitating a change in the character of the reactions of 

 the ameba. This makes it clear that any (|ualit\' whicli necessarily 

 attaches to an\- solid object is not the t|uality that stimulates the 

 ameba from a (Hstancc; tlu- ([uality that stinuilates the ameba is 

 one that is common to the ])article of glass and the beam of light. 



