4&2 



NATURE 



[September 8, i 904 



sixth cervical root, it is almost always flexion. Yet although 

 the same root may thus be made to evoke reflex action of the 

 flexors or of the extensors, I have never seen it evoke contrac- 



tu i. 2 —Interference between the reflex action of the left hip flexor, fc, caused by the nervous arc from the 

 left foot (L, Fig. I B)and the scratch reflex. The stimulation of the dorsal skin (Fig. i A) inducing the 

 scratch reflex began at the beginning of the notch in the signal line s, and continued throughout the 

 period of that notch. Later, for the period marked by the notch in the signal line l the stimulation 

 of the foot was made. This latter stimulation interrupts the clonic scratch reflex in the manner shown. 

 The time is registered above in fifths of seconds. The tracing reads from left to right. It is note- 

 worthy that the interruption of the scratch reflex by the foot reflex is not established directly the 

 foot stimulus begins, and that it outlasts for a short time the application of the foot stimulus. 



tion in both fle.xors and e.xtensors in the same reflex response. 

 Of the two reflexes on extensors and fle.xors respectively, 

 either the one or the other results, but not the two too'ether. 



NO. 1 819, VOL. 70] 



Good opportunity for study of this correlation between 

 efle.xes is given in the " scratch reflex." When the spinal 

 ord has been transected in the neck, this refle.x in a. few 

 months becomes prominent. Stimuli 

 applied within a large saddle-shaped 

 field of skin (Fig. i K) excite a 

 scratching movement of the leg. The 

 movement is rhythmic flexion at hip, 

 knee, and ankle. It has a frequency 

 of about four per second. The stimuli 

 provocative of it are mechanical, 

 such as rubbing the skin, or pulling 

 lightly on a hair. The nerve-end- 

 ings which generate the reflex lie in 

 the surface layer of the skin, about 

 the roots of the hairs. A convenient 

 way of exciting these is by feeble 

 faradisation. A broad diffuse elec- 

 trode is applied to some indifferent 

 part of the surface elsewhere, and a 

 stigmatic pole is brought to some 

 point in tile saddle-shaped area of 

 dorsal sl-Lin. This pole is formed by 

 a minute needle with fine wire 

 attached ; it is set lightly, so that its 

 point just lies among the hair-bulbs. 

 Prominent among the inuscles 

 active in this reflex ate the flexors 

 of the hip. If we record their 

 rhythmic contraction we obtain 

 tracings as in Figs. 2, 3, 4. A 

 series of brief contractions succeed 

 one another at a certain rate, the 

 frequency of which is independent of 

 that of the stimulation. The con- 

 tractions are presumably brief tetani. 

 The stimulus to the hair-bulbs of the 

 shoulder throws into action a lumbar 

 spinal centre, innervating the hip- 

 flexor much as the bulbar respiratory 

 centre drives the spinal phrenicus 

 centre. In the case of the respir- 

 atory muscle the frequency of the 

 rhythm is, however, much less. 



This reflex is unilateral ; stimu- 

 lation of the left shoulder evokes 

 scratching by the left leg, not by the 

 right. Search in the spinal cord for 

 the path of the reflex demonstrates 

 that a lesion breaking through one 

 lateral half of the cord anywhere 

 between shoulder and leg abolishes 

 the ability of the skin of that shoulder 

 to excite the scratch reflex, but leaves 

 intact the reflex of the opposite 

 shoulder. 



In the lateral half of the spinal 

 cord which the reflex path descends, 

 severance of the dorsal column does 

 not interfere with the reflex ; nor 

 does severance of the ventral and the 

 dorsal columns together of that side ; 

 no more does severance of the grey 

 matter in addition. But severance of 

 the lateral part of the lateral column 

 itself permanently abolishes the con- 

 duction of the reflex ; and it does so 

 even if all the other parts of the cord 

 remain intact. The path of the 

 reflex therefore descends the lateral 

 part of the lateral column. 1 enter 

 into these details because they help 

 toward the construction of the reflex 

 arc involved. For in the lateral part 

 of the lateral column one has proved 

 by " successive degeneraiion " that 

 litng fibres exist directly connecting 

 the spinal segments of the shoulder 

 with the spinal segments containing the motor neurones 

 for the flexor muscles of the hip, and knee, and ankle. The 

 course of these long fibres can be traced and their number 



