1893.] the Normal State of the Knee Jerk is altered. 451 



IV. Intracranial Division of the 8th Nerve on one Side. (Control.) 



No inequality in the knee jerks was produced, either at the time of 

 the operation, during the few hours immediately following the opera- 

 tion, or at any time during the week, after the section of the 8th 

 nerve. 



V. Chemical Irritation of the 8th Nerve on one Side. (Control.) 



It was found impossible to expose a sufficient length of the nerve 

 to apply an irritant to it without lifting up the lateral lobe of the 

 cerebellum. As any interference with the cerebellum would have 

 vitiated the experiment, it was decided that, instead of applying the 

 irritant directly on the nerve, it should be placed in the labyrinth 

 instead. Accordingly the labyrinth was opened, and a small portion 

 of the 8th nerve exposed as it entered the labyrinth. Crystals of 

 chloride of sodium were next carefully packed around the stump of 

 the nerve and kept in position by means of a plug of aseptic wool 

 introduced into the labyrinth. The knee jerks were carefully tested 

 immediately after the operation, and frequently during the same day, 

 but no alteration could be detected in them, and they remained 

 normal and equal on the two sides during the week that they were 

 kept under observation. 



SUMMAET AND CONCLUSIONS. 



I. The Effects of Asphyxia. 



The results obtained in asphyxia appear to be due in great measure 

 to cutting off: the supply of oxygen to the lumbar centres. The pre- 

 liminary exaggeration of the knee jerk might have been due to the 

 taking off of cortical control from the lumbar centres, letting them 

 go, so to speak, as suggested by Hughlings- Jackson,* for, as numerous 

 experimenters have shown, asphyxia diminishes, and in an extreme 

 degree annuls, the excitability of the motor cortex. That this hypo- 

 thesis cannot be entertained is proved by the following facts. At the 

 time when the knee jerk first becomes exaggerated the excitability 

 of the motor cortex is little, if at all, diminished, and is not annulled 

 until a considerable time after the knee jerk is abolished. Further, 

 and this appears to me more conclusive evidence, the same exagger- 

 ation of the knee jerk was met with when asphyxia was induced in 

 animals whose spinal cords were divided above the lumbar enlarge- 

 ment, in which case any cerebral influence was entirely put out of 

 court. As far as the preliminary exaltation of the knee jerk is con- 



* 1 Brit. Med. Journ.,' February, 1892. 



