238 bulletin: museum of compaeative zoology. 



mission would be 0.0033 second, leaving a remainder of 0.0035 second 

 for tlie latent time of muscular contraction. 



The results of the above investigations of physiological time do not 

 reveal the normal reaction-time. The physiologists, in studying the time 

 relations of neural processes, have begun from within, and by stimulating 

 the different parts of the brain have attempted to learn how the time 

 occupied in eflerent transmission is distributed among the brain regions. 

 The psychologists, on the other hand, have attempted to measure the 

 normal reaction-time to stimuli of peripheral sense-organs. The results 

 of the physiological method permit of a fui'ther time analysis, as I have 

 shown above; the results of the psychologists cannot be so analyzed. 

 Much work has been done by the psychologists in determining the reac- 

 tion-time of man, but practically nothing has been done on the lower 

 animals. Yerkes (: 02) has, however, done valuable work of this kind 

 on the frog. He finds the normal reaction-time of the frog to tactual 

 stimuli to be about 0.2 second, or about twice as great as in man. The 

 reaction-time to comparable electrical stimuli is somewhat less. He was 

 unable to measure the reaction-time to optical stimuli. 



b. Delay in Transmission through the Cell Body. 



It has been conclusively shown by S. Ramon y Cajal and by Bethe ('97) 

 that in some nervous processes the impulse is not necessarily transmitted 

 through the cell body. Bethe ('97) has proved in Carcinus that trans- 

 mission may even take place normally when the fibres have been severed 

 from tiieir ganglion cells. But it is doubtless e(jually true that in the 

 great majority of central processes the nervous impulse is transmitted 

 through the perikaryon. It is commonly assumed that in the trans- 

 mission of a nervous impulse through the cell body, the impulse is 

 delayed, though the evidence on this point is not wholly conclusive. 

 Wundt ('76, Abth. 2, p. 45) found a delay of 0.02 second in transmission 

 through the spinal ganglion of the frog. Doubt has been thrown on this 

 result by Exner ('77, p. 567), who has pointed out that the nerve-impulse, 

 in passing through the posterior roots, is not transmitted through the 

 cell b(jdy, as Wundt supposed ; and Moore and Reynolds ("98, p. 56), 

 repeating Wundt's experiments, have shown that when in two experi- 

 ments the path of the impulse through the cord was the same, the inter- 

 position of the ganglion caused no appreciable delay. When, however, 

 the impulse is obliged to traverse the cell body, a delay occurs. Gad 

 ('89) showed " that the interposition of the vagus ganglion caused a 



