230 A. A. SCHAEFFER 



left behind. It is uncertain whether the indigotin had been 

 completely ingested. 



The experiments recorded in this section demonstrate con- 

 clusively that amebas respond positively to mechanical stimula- 

 tion. Food objects when mechanically agitated, are more readily 

 eaten than when lying quiet, and in many cases food objects are 

 not eaten at all unless they are in motion. Further, insoluble 

 objects, like glass, are not eaten when lying quiet, but when 

 agitated properly they are readily eaten. It is not necessary 

 for a solid object to come into contact with the ameba in order 

 that a food cup may form; vibrations of the water are quite 

 sufficient to produce the feeding reaction. A chemical stimulus 

 is therefore entirely unnecessary in order to set off the feeding 

 reaction. Movement is not only a contributing factor but it 

 is in itself an efficient factor in calling forth the feeding process. 



It will be noted that when vibrated particles are eaten, they 

 are seldom retained for more than a few minutes, whether they 

 are of food value or not. The reason for the speedy excretion 

 of such particles is that the chief, if not the only quality of the 

 particle which mcited the feeding process, movement, disappears 

 when the food cup closes, for mechanical vibration is then no 

 longer possible. Since the most attractive quality suddenly dis- 

 appears, the feeding process stops before it is entirely completed. 

 The formation of a food cup resembles to some extent a reflex 

 act: when an agitated particle of glass is eaten, the formation 

 of the food cup continues for some time after the vibrations have 

 ceased. The formation of food cups is due to a racial habit 

 which is guided to a greater or less extent by circumstances 

 attending the formation of a cup at any particular time. Since 

 circumstances vary greatly, one observes great diversity in the 

 behavior toward particles which produce positive reactions. 



Whether the swallowed particle is retained or speedily excreted 

 is largely independent of the character of the feeding reaction. 

 The food cup may have been perfectly formed and yet the par- 

 ticle inciting it may be speedily excreted; or on the other hand, 

 the food cup may have been very imperfect, but the particle 

 may be retained. The retention of a vibrated particle in the 

 ameba seems to depend on qualities other than those which 

 caused ingestion. What such qualities are cannot be definitely 

 stated. The composition of the particle seems to have relatively 



