EFFECT OF ADRENIN UPON RATE OF LOCOMOTION. 163 



animals which showed to a greater extent the symptoms of 

 excitement were those which had been treated with adrenin for 

 an hour or less. Those which were in the solution for a day, with 

 the exception of some of the groups of Table I., Series 3, showed 

 almost uniformly a real slowing of the rate of muscular contrac- 

 tion. It may be that the initial effect produced by adrenin 

 upon the muscular apparatus of planarians is excitatory in nature, 

 and that the increased irritability, expressed in useless and non- 

 coordinated movements really results in a decrease in the rate 

 of locomotion. As the animals are left in the solution, however, 

 the exciting effect wears off, and there results either an approxi- 

 mate return to normal, as in Series 3, Groups C and E, or a 

 decrease in irritability, following naturally the undue excitement 

 created at first. 



This hypothesis of an initial excitatory effect might account 

 also, for some of the other discrepancies of Series 3. The animals 

 of Groups A and D, which showed such a poor initial rate in 

 water may have been in a condition of lowered vitality, perhaps 

 a state of fatigue. Here, as the results show, there followed an 

 increased rate after treatment w r ith adrenin. Might it not be 

 possible that the excitatory effect of the extract was, in these 

 cases, merely sufficient to raise the muscular tone to normal, 

 without producing any symptoms of over-excitation? It is not 

 unlikely that in these animals the increase in the rate of locomo- 

 tion indicates the real effect of adrenin, which in most of the 

 other experiments is marked by the decrease in rate due to the 

 useless movements of excitement. This possibility may be 

 lessened, perhaps, by the fact that the animals of Group A 

 continued to improve even more after return to water, while 

 those of Group D fell back, indicating that other factors were 

 at work; but this does not exclude the view that adrenin produces 

 a temporary improvement which may .or may not become more 

 lasting, dependent upon these other factors. 



In order to determine w r hether or not the same results are 

 produced by repeated doses of adrenin, several further tests 

 were made, the results of which are recorded in Table II. After 

 each treatment with the extract, one to three days in water 

 were allowed for recovery before the next tests were made. 



