1893.] the Normal State of the Knee Jerk is altered. 439 



stretching (moderately and gently) a hamstring muscle would pro- 

 duce the same effect, thus proving that afferent impulses from the 

 hamstrings normally inhibit the jerk. 



The General Plan of Research. 



In the present research various circumstances under which the 

 knee jerk is altered are dealt with, and may, for convenience of 

 description, be best arranged in two large groups. 



A. Those circumstances under which the alteration in the state of 

 the knee jerk is brought about by some influence locally exerted on 

 the lumbar centres. 



B. Those circumstances under which the alteration is due to some 

 remote cause. In the first of these groups are included : — 



I. The effects of asphyxia. 



II. The effects of the inhalation of certain gases (nitrogen, nitrous 



oxide, and oxygen). 



III. The action of anaesthetics (ether and chloroform). 



IY. The effect of anaemia of the spinal centres as brought about 

 by compression of the abdominal aorta, or by general loss of 

 blood. 



V. The action of intravenous injections of absinthe and strychnia 



respectively. 



VI. The result of bisection of the spinal cord made vertically at 



the level of the centres in which the knee jerk appears to be 

 represented. 



The second group includes : — 



I. The effect of removal of a cerebral hemisphere. 



II. The immediate and late effects of extirpation of different parts 



of the cerebellum. 



And as control experiments in this connexion. 



1. The effects of extirpation of the labyrinth. 



2. The effects of intracranial section of the 8th nerve. 



3. The effects by chemical excitation of the 8th nerve. 



In every instance those circumstances under which the knee jerk is 

 exaggerated, and those under which it is abolished, are considered ; 

 but, inasmuch as both conditions may be brought about during 

 different stages of the same influence, both of these states of the knee 

 jerk are considered together. 



