40C) MEMOIRS OF THl-: NATIONAL ACADEMY OF SCIENCES. 



"warraut; Imt in this case tbt- piobable error is a comparatively small part of tlie whole time, and 

 the ditt'ereiice is undoubtedly due to the difterent pointof application. It remains an open question 

 whether the cerebral reflex miglit not be shorter wlien the stimulus is applied to the arm, in which 

 case the times would not measure the velocity in the sensory tracts of the spinal cord. Indeed, 

 this seems to be proved by the fifth line in the table, which gives the ditt'ereuce in time when the 

 movement was made with the foot and the stimulus applied to the lower leg and lower arm, 

 respectively. In this case the difference in time (with a rather large probable error for C) was for 

 D 18.9 I), for C 18.7 c. The excess of distance in the spinal cord was the same as before, but the 

 times are about 8 a shorter. We are enabled, consequently, to draw the interesting conclusion that 

 when the stimulus is applied to the left arm the cerebral reflex is 8 <? shorter when the movement is 

 made with the arm than when made with the leg and conversely. The sensory fibers from one 

 part of the body are most closely connected with the motor fibers to the same part.. 



We conclude, with some confidence, that when a stimulus is applied so that the impulse must 

 traverse the spinal cord and from the lumbar to the brachial plexus the time of reaction is about 

 2() a longer when the movement is nnide with the hand and about IS a longer when the movement 

 is made with the foot. The difference in the two cases is due to greater rapidity of the central 

 reflex owing to closer connection in the brain between sensory and motor fibers from the same 

 part of the body. If the whole excess of time in the case compared be due to transmission in the 

 cord we should have a velocity of about 15 meters per second in the sensory tracts of the si^inal 

 cord. The velocity is at least not less than this. 



Tliere remains for consideration the difference in the time of reaction when the movement is 

 made with the hand and foot, respectively. When the stimulus was applied to the lower arm the 

 ditterence was for D 37.7 a and for C .54.4 a; when the stimulus was applied to the lower leg 

 the difference was for D L'9.7 a and for C 45 6. The difference was less (D 8 c and C 9.4 ff) when 

 the stimulus was applied to the leg, and by almost exactly the same amount as before. We have 

 evidently measured the diflcreiice in time of the cerebral reflex when the motor impulse proceeds 

 to the part of the body from which the sensory impulse arrives, and when it proceeds to a different 

 part. The differences in the times when the reaction is made with hand and foot are partly due 

 to the time rec^uired to ti-averse the motor tracts of the spinal cord, but they may also be due to 

 differences in the cerebral processes. The cerebral reflex is undoubtedly less perfect for the foot 

 than for the hand. The difference in the case of the two observers (lfi.3 a greater for C) is almost 

 certainly a difference in the cerebral process. C's reaction with the hand is very automatic; with 

 the foot it is more nearly like D's. How much of the delay is due to traversing the motor tracts' 

 between the brachial and lumbar plexus can not be decided. If the whole time in the case of D 

 were so consumed (ignoring the difference in the plain nerve) the velocity of transmission would be 

 about 19 meters per second, and this is at least a minimum velocity. In so far as we can accept 

 these results the velocity in the sensory tracts of the cord would be greater than in the motor 

 tracts. This difference in velocity might be explained by the partial coordination of the move- 

 ment in the cord. The difference, however, may be equally well attributed to the delay of 

 coordination in the brain centers. 



In view of the fact that the velocity in the sensory nerve had not been determined in a 

 satisfactory manner, owing partly to the varying physiological effects of the shock on the points 

 stimulated, we sought for a point on the lower arm for which the sensation should be as nearly 

 .as possible the same as on the point D of the upper arm. The best place we could find was a point 

 3 cm. below B and a little on the side of the line of the median nerve, as shown in fig. G, the 

 point being marked A. The stinuilation of this point was followed by a strong contraction of 

 the thumb and a massive sensation similar to that following the stimulation of the point I). We 

 also chose a point, C (fig. G), on the line of the median nerve, the stimulation of which was 

 followed by a sensation similar in quality to that from the point B. This point was 20 cm. above 

 B and Id cm. below D. In Table II are given the reaction-times when the points A and B were 

 alternately stimulated; also reactions in which the current was from electrodes 5 mm. ajjart, 

 ■when on opposite sides of the limb, and when it passed through the body to the fiwt. 



