1893.] the Normal State of the Knee Jerk is altered. 445 



that the knee jerk remains absent depends entirely on the depth of 

 narcosis, and the length of time this is continued, these bearing a 

 direct ratio to each other. The exaggeration of the knee jerk which 

 has been alluded to is never so pronounced as in simple asphyxia or 

 the condition induced by nitrogen or carbonic oxide ; but it is never- 

 theless perfectly distinct. 



2. Chloroform. — The results obtained were identical with those 

 obtained with ether, with two important exceptions, however; thus, the 

 knee jerk is lost very much more rapidly under its influence than 

 under the influence of ether, and after the administration of the 

 narcotic is discontinued a longer period elapses before the knee jerk 

 shows any sign of returning than after a similar depth and duration 

 of ether narcosis. 



These effects with ether and chloroform were obtained both when 

 the spinal cord was intact and when it had been previously divided 

 transversely in the mid-dorsal region. 



IV. The effect of Anaemia of the Spinal Centres as brought about by 

 Compression of the Abdominal Aorta or by General Blood-letting. 



1. Compression of the Abdominal Aorta. — This was effected by 

 means of the thumb, either through the structures composing the 

 abdominal wall in the rabbit, or after the artery had been exposed by 

 dissection (rabbit and dog). The resistance offered by the bony 

 spinal column makes it exceedingly easy to entirely stop the flow of 

 TDlood in the aorta beyond the point at which compression is made by 

 the thumb. As Prevost* found, after the compression had been kept 

 up a short time the knee jerk disappeared, and the time that it con- 

 tinued absent after the compression had been taken off varied directly 

 as the time that the compression had been maintained ; the longer 

 the compression, the longer did the knee jerk afterwards take to 

 return. Before the knee jerk was abolished, and after it was 

 abolished and before it returned to its normal state, it passed through 

 stages of exaltation, as has been already observed to be the case in 

 other conditions attended with loss of the knee jerk. 



2. General Blood-letting. — The carotid artery was opened on one or 

 other side, and the animal allowed to gradually bleed to death. As 

 more and more blood was lost so the knee jerk became more and 

 more active at first; but after a time it gradually became less so, 

 until it eventually disappeared entirely, and did not reappear up to 

 the time of tbe death of the animals. 



* Loc. c't. 



