Transinis.sioii-time of Reflexes in Spinal Cord of Frog 7 



second effect occurred, l)ut in each it occurred at the same time after the 

 hrst. It did not show itself in any of the responses to the just maximal 

 stimulus. That the second effect, which (in records taken without the aid 

 of a drug to increase the excitability of the cord) was seldom larger than in 

 this experiment, is the reflex effect is perhaps more convincingly showna by 

 the records obtained when the second method of experiment was employed. 

 This consisted in first recording the response when the nerve was 

 excited by a stimulus five or ten times as strong as would probably be 

 required to produce a maximal response to excitation of the motor nerve. 

 Then, after obtaining not more than four records of this response, one of 

 which was taken with the direction of the induction current reversed, the 



Fig. 1. —First and second electrical responses of the gas- 

 trocnemius of a normal preparation, obtained when 

 the intact sciatic nerve of the same side was excited : 



A, by a stimulus which was little more than just maximal 

 (1000 units). [Time lines 760 per second.] B, by a stimulus 

 of three times the strength. | Time lines 730 per second.] 



sciatic nerve was divided between the exciting electrodes and the cord, and 

 the response obtained when the peripheral end was excited by the same 

 supra-maximal stimulus applied to the same spot on it was recorded two or 

 three times. The small second effect which was sometimes there in all the 

 records taken with the nerve intact was never seen after its severance from 

 the central nervous system. The disadvantage of this method is that one 

 cannot alternate the two things which have to be compared as one can 

 with the other method ; and since the reflex efl'ect disappears long before 

 the direct effect, seldom being obtainable in a normal preparation in 

 response to more than a very few excitations of the mixed nerve, it is 

 important in using it to excite as few times as will suflice to make 

 absolutely sure that the effect, if present, is by no possibility accidental, 

 and to ascertain the time of its occurrence, before dividing the nerve. 



