MODIFICATION OF THE BEHAVIOR OF LAND ANIMALS 43 



minute period (C), the toads were transferred (as before) to the 

 control cage. After a few moments they began to show a 

 preference for the same end that was preferred in the preceding 

 period. While controls sometimes show asymmetry, this is the 

 only one out of ten which shows any such peculiarity. 



In the table, the items marked B, C, D, under Bufo, repre- 

 sent two experiments and the control which followed them. 

 In the first experiment (Column 9) the number of trials before 

 turning back was 2.6 and the time over 200 seconds in the highest 

 and lowest evaporation. In the second experiment the trials 

 were reduced to 1.0 and the time to a little more than 80 seconds. 

 In the control observation which followed, they showed a prefer- 

 ence for the end corresponding to the moist air with less trials 

 and with less time than was required in the first experiment. 

 Toads have no tendency to come to rest in one end, or in contact 

 with the walls. The two sides of the cage were not exactly 

 alike and the toads could perhaps sense the screen on their right 

 or the lights in front when approaching the end in which the 

 high evaporation occurred in the experiments. The one experi- 

 ment suggests that the toads may have associated the lights 

 ahead or the view through the screen with the dry air further on 

 (see Fig. 1). 



IV. INTERPRETATION OF RESULTS 



Protoplasm and the plasmas of organisms possess a definite 

 mechanism for maintaining approximate neutrality. ' Neu- 

 trality is quite as definite, quite as fundamental and quite as 

 important a characteristic of the organism as its temperature, 

 or osmotic pressure, or in fact anything else we know" (Hender- 

 son, '13a). 'Within wide limits of amount any acid or base 

 may be poured into the organism and the reaction will not 

 vary," nor will it vary if such be produced by the organism. 



In the preceding paper we noted that presenting acid either 

 externally or internally produced increased sensibility or in- 

 creased irritability. By this we do not mean to suggest that 

 any particular degree of acidity was probably attained except 

 where staggering occurred, but rather that a tendency toward 

 acidity occurred during the adjustment of the neutrality mech- 

 anism. Just what the relation of the ammonia to the neutrality 

 mechanism is in the case of fishes and other vertebrates is not 



