1893.] the Normal State of the Knee Jerk is altered. 447 



absinthe had been injected, and did not again disappear in the course 

 of half an hour, during which time it was under careful obser- 

 vation. 



2. Strychnia. — The effect of this drug was only tested in the dog. 

 Two minims of a 1 per cent, solution of strychnia were injected into the 

 femoral vein, after the spinal cord had been previously divided trans- 

 versely in the mid- dorsal region. Powerful convulsions quickly 

 followed in all parts whose nerve supply was derived from above the 

 cord lesion, while those whose nerve supply was from below this point 

 remained free from convulsion. The knee jerk was increased at first 

 slightly, but soon more so, and on injecting 1 minim more of the 

 same solution of strychnia into the femoral vein as before, a single 

 tap on the patella tendon was sufficient to evoke tonus in the 

 quadriceps extensor. 



When strychnia was administered without the spinal cord being 

 previously divided, general convulsions of course resulted, and these 

 seriously interfered with the observations on the knee jerk, as even 

 when the animal was not in a comparatively quiescent state a tap on 

 the quadriceps tendon usually sufficed to evoke convulsions. The 

 plan of first dividing the spinal cord transversly in the dorsal region 

 was therefore that usually adopted in observing the effects of strychnia 

 on the knee jerk, and in all cases there could be no question as to the 

 increase of the jerk under the influence of this drug. 



VI. Tlie Results of Section of the Spinal Cord. 



1. Transverse Section. 



2. Vertical Section. 



1. Transverse Section of the Spinal Cord. — It has long been recog- 

 nised that in the lower animals complete transverse section of the 

 spinal cord above the level of the lumbar enlargement is followed by 

 increased activity of the knee jerk. My own experiments in the dog 

 show that the immediate effect of such a lesion depends on the depth 

 of narcosis. The cord was always divided at or about the mid-dorsal 

 region, and in no instance did the knee jerk disappear after such 

 section of the cord when there had been no doubt as to its presence 

 before the lesion was inflicted, while usually there was no difficulty 

 in being certain of its increased activity under such circumstances. 

 The depth of ether narcosis, however, plays a most important part in 

 this connexion, for if the cord were divided when narcosis was so 

 profound that the knee jerk was almost abolished, the section of the 

 cord hastened the result ; and when the cord was divided jvhen the 

 depth of narcosis was such that the knee jerk was abolished, the 

 latter remained absent for a much longer time than is usual after 



