FOOD-EEACTIONS OF AMEBA PROTEUS 411 
regions, if not completely protected from the waves that radiated 
from the Chilomonas, were much less stimulated than was the 
broad end of the parent pseudopod; in addition to this, the 
smaller of these secondary pseudopods lay nearer the Chilomonas. 
This should have been the larger had the reaction been a quan- 
titative one. Moreover, this reaction presents another inter- 
esting phase, for after it had well set in, a second Chilomonas 
entered the bay between the advancing secondary pseudopods. 
The amplitude of the water's agitation must now have been 
relatively greatly increased and yet the conduct of the two small 
pseudopods was not altered and they finally converged, though 
the stimulus had been increased. Here the qualitative character 
of the reaction is displayed in a manner exactly the opposite of 
that in which Kepner and Edwards ('17) saw a Pelomyxa act 
in a qualitative manner toward Paramecium, where, ''though 
the stimulus was weakened the pseudopods continued to diverge 
as they grew" (p. 394) about the remaining Paramecium of the 
three that were present at the inception of the reaction. Because 
of the qualitative character of the ameba's food reactions, it 
appears to us that these reactions toward an animal that presents 
the possibility of escape are modified with reference to meeting 
that contingency. The ameba's reactions differ, therefore, from 
chemical reactions in that they are made in the interests of the 
ameba and may be suspended or even reversed when its own 
interests demand. 
SUMMARY 
1. There are two general types of reaction to food: a) when no 
contingency of escape is presented by the prey, the ameba tightly 
surrounds the food; h) when such contingency is presented, a 
wide embrace is made and the prey is disturbed only when 
retreat is cut off. 
2. These two types of food reaction are not fixed, but vary 
greatly. 
3. In reacting to an object that usually moves in a horizontal 
plane, the ameba surrounds the prey in this plane first and next 
cuts off its vertical paths of escape. 
