Io8 Asa Arthur Schaejfer 



the apparatus for receiving stimuli has not become effectively 

 fatigued. 



Thus it appears clear that the occurrence of loops is not due to 

 fatigue; we must look for the explanation in some other change in 

 the physiologic state of the animal. As noted above, the loops 

 appear as the animal approaches satiety, so that there can be little 

 doubt but that the change in the degree of hunger is whatbrings 

 on the loops. The loops, as we have seen, almost always occur 

 in the paths of particles that are finally rejected. It appears that 

 the rejecting mechanism is not set m operation by the first slight 

 stimulus from an objectionable particle, but the stimulus seems 

 to be summated with every successive loop that is made, until it 

 is finally strong enough to cause rejection. In the first stages 

 when the animal is hungry the ingesting mechanism is more readily 

 set ofi- than that for rejection; near repletion, the rejection appa- 

 ratus is more readily set off; and as repletion advances the reject- 

 ing apparatus is continually more and more readily set off, re- 

 quiring therefore fewer loops. The apparatus for receiving stim- 

 uli seems therefore to be in a state of continual change, so that 

 stimuli which readily set off the ingesting reaction when the ani- 

 mal is hungry have but a slight effect when the Stentor is nearly 

 replete, and finally have no effect at all, or set off only the rejecting 

 reaction. 



A difference is seen in the fact that when a particle is accepted, 

 tnis is done (as a rule) at once, without loops, while rejection is 

 done only after some delay, with the occurrence of loops. Only 

 when the Stentor is fully satiated does rejection occur instan- 

 taneously. In the state of incomplete satiety, rejection is a slow 

 and uncertain process, as if the stimulus for rejection had first to 

 gather strength before rejection could occur. 



Thus the number of loops which occur before rejection depends 

 on the degree of hunger. There is doubtless a similar though 

 reverse effect of hunger on the ingesting apparatus; it seems cer- 

 tain that a stronger stimulus is required to set off the ingesting 

 reaction when the Stentor is partially satiated than when very 

 hungry. But the evidence is not so clear as for the rejecting 

 apparatus owing to the fact that loops rarely occur in the path of 



