442 Mr. J. S. E. Russell. Circumstances under which [May 18, 



A. Circumstances under which the Alteration in the State of 

 the Knee Jerk is brought about bt some Local Action on 

 the Lumbar Centres. 



I. The Effects of Asphyxia. 



Asphyxia was produced either by clamping a short piece of india- 

 rubber tubing fixed to the free extremity of the tracheotomy tube, or 

 by inserting an india-rubber plug into the tracheotomy tube directly. 

 Before inducing asphyxia the knee jerks were carefully and repeatedly 

 tested in order to be certain that the depth of narcosis was not such 

 as to cause any material alteration in the state of their condition. 

 When it was satisfactorily determined that they were as nearly as 

 possible normal, cardiac and respiratory tracings were taken for some 

 seconds before the tracheotomy tube was plugged. The immediate 

 effects on the respiratory and cardiac movements do not call for 

 description ; that they were those usually met with under similar 

 conditions is shown in fig. 1. 



1. The Effects of Asphyxia on the Lumbar Centres with the Spinal 

 Cord Intact. — The first effect which the altered conditions of the 

 blood had on the knee jerk was to cause it to become exaggerated ; 

 this quickly became more and more marked, until clonus at the knee 

 was produced by a single tap on the patella tendon ; and when the 

 exaggeration was at its maximum a tap on one tendon not only pro- 

 duced clonus on that side, but also evoked the knee jerk on the 

 opposite side, even to the extent of a few clonic jerks. After this 

 stage was reached the knee jerk became less and less marked, until 

 it disappeared completely, and did not return up to the time of the 

 death of the animal, when this was allowed to take place. But if, 

 instead of allowing the animal to die, the obstruction to the entrance 

 of air into the lungs was removed, and the animal recovered 

 either with or without the aid of artificial respiration, the knee jerk 

 reappeared. The time which elapsed before its reappearance de- 

 pended on the length of time that the asphyxial state had been kept 

 up ; the shorter the duration of this state the quicker did the knee 

 jerk return, and vice versa. On its return the knee jerk did not at 

 once present its normal characters ; at first feeble, it quickly passed 

 into a state of exaggeration, sometimes to the extent that a single 

 tap on the patella tendon evoked a few clonic jerks ; after a variable 

 period this exaltation subsided, and it returned to its normal condi- 

 tion. The stages in the asphyxial state to which these different 

 phenomena are related are indicated in fig. 1, which shows the 

 respiratory and heart tracings obtained from a dog. About 2 minutes 

 after the trachea was clamped the stage of asphyxial convulsions 

 was reached, and after the blood pressure had risen the knee jerk 



