484 H. S. Jennings. 



B, producing a bending to one side. After several repetitions 

 of the stimulus, the state B passes to the state C, producing 

 a reversal of the cilia, and this finally passes to D, resulting in a 

 contraction of the body. Each state must of course be difi^erent 

 from the preceding one, because it produces a different result. 

 The course of the changes in physiological states may then be 

 represented as follow^s : 



A »B >C »D 



Now we find that after many repetitions of the stimulation the 

 animal contracts at once as soon as the carmine comes in contact 

 with it. In other words, the first condition A (direct result of 

 contact) passes at once to the state D, and this results in imme- 

 diate contraction: 



A ►D 



It seems probable that the same series occurs as before, save 

 that B and C are now passed rapidly and in a modified way, so 

 that they do not result in a reaction, but are resolved directly into D. 

 The process would then be represented as follows: 



A — . B' — > a ► D 



But whatever the intermediate conditions, it is clear that after 

 the state A has become resolved, through pressure of external 

 conditions, into the state D, this resolution takes place more 

 readily, occurring at once after state A is reached. 



The same law is illustrated in the experiments of Yerkes and 

 Spaulding on association in crabs. In the experiments of Spauld- 

 ing ('04) with hermit crabs, the introduction of the dark screen into 

 the aquarium, and the diff'usion of the juices of the fish, cause the 

 animals to move about. In so doing they reach the dark screen, 

 which induces, let us say, the physiological condition A. This 

 leads to no special reaction. But this is followed regularly by 

 contact with food, inducing the physiological state B, which is 

 concomitant with a positive reaction. The physiological state A 

 is thus regularly resolved into the state B. In the course of time 

 this resolution becomes automatic, so that as soon as the state A 

 is reached, it passes to B. The positive reaction concomitant with 

 B is therefore given even though the original cause of B is absent. 

 The actual number of physiological states which could be dis- 



