562 Dr. C. S. Sherrington. On the Knee-jerk and the [Feb. 9, 



position of the knee joint or affect it mechanically. This precaution 

 was observed by isolating the two inner hamstrings from their 

 attachments, except at their origin, from the tuber iscliii, and simul- 

 taneously cutting through all nerve branches to the outer hamstrings 

 and to the adductor muscles. The nerves to the inner hamstrings 

 were carefully preserved although the muscles were otherwise dis- 

 sected out. It was found that by pulling on the inner hamstring 

 muscles sufficiently to stretch them out of the doubled-up shape they 

 assumed after being freed from their lower attachments, the knee- 

 jerk, previously brisk, was at once abolished or greatly diminished, 

 and on relaxing the strain on the hamstring muscles at once re- 

 appeared, and was apparently somewhat more brisk than before the 

 diminution. It is often sufficient to merely compress the hamstring 

 muscles, as they lie flaccid on the hand, between fingers and thumb. 

 A kneading of the muscle as in massage has the same effect. On 

 two occasions, at the end of an experiment, when the muscles had 

 suffered from exposure, I have seen the curious phenomenon that ex- 

 citation of a motor root supplying them of strength insufficient to 

 throw the injured muscles into obvious contraction yet suffices to at 

 once cut out the "knee-jerk," although before and after the excita- 

 tion the "jerk" was very brisk indeed. The effect was obtained 

 several times in succession, and immediately disappeared on dividing 

 the sensory roots coming in from the exposed muscles. The current 

 of injury in the muscles must have been considerable, and this suggests 

 that the mere negative variation of the current of injury in the 

 muscles might originate centripetal impulses. Certainly there was 

 on neither occasion any obvious contraction in the muscles. 



The most efficient mode of excitation of the afferent fibres from 

 these muscles appears to be the mechanical above described, i.e., the 

 myotatic (Gowers).* 



Excitation of the central end of the divided popliteal or peroneal 

 nerves does not produce this effect upon the jerk. Neither does 

 stretching of the crural triceps by pulling on the tendo Achillis, nor 

 stretching of the rectus femoris muscle. Stretching of the rectus 

 femoris can easily be employed without interference to the movement 

 of the knee joint. It appears to me neither to increase nor to 

 diminish the jerk. Excitation of the central end of the divided nerve 

 to the rectus femoris exerts likewise no obvious influence on the 

 jerk ; nor does excitation of the central end of the cutaneous divisions 

 of the anterior crural, viz., the internal saphenous and the internal 

 and middle cutaneous nerves of the thigh. Excitation of the central 



* Diagnosis of Diseases of the Spinal Cord/ 2nd edit., 1881, p. 29. See also 

 the same author's " Diseases of the Spinal Cord,' vol. i, p 21 also pp 202205 

 428, 429, 2nd edit., 1892. 



