160 



Mr. Graham Brown. 



[Nov. 12, 



in walking ; or of very nearly perfect bilateral synchronism — as in the 

 gallop. Its narcosis progression may take either form. 



The great part played by the flexor muscle is a point of interest. It must 

 be remembered that the movements of extension are much more affected by 

 chemical narcosis than are those of flexion. It is perhaps because of this 

 that when the individual muscles are examined the flexor alone appears to 

 take part in the movements. It is probable that the extensor does take part 

 in the better marked types of narcosis progression, although it is difficult to 

 shew that it does. That muscle certainly takes part in the phenomena of 

 progression which follow mechanical stimulation of the spinal cord and are 

 extremely like the movements of narcosis progression. It also takes part in 

 many instances of the rhythmic rebound phenomenon, which again is very 

 similar to these two types of movement. But it is equally clear that the 

 phenomenon of narcosis progression may appear when there is no evident 

 contraction of the extensor at the ankle. 



Again, the independence of the flexor centre is a point of great interest. 

 The movements of narcosis progression may be present after decerebration. 

 They may persist even after the isolation of the aboral part of the spinal 

 cord by division in the lower thoracic region. The phenomenon of narcosis 

 progression may therefore be conditioned by the lumbar centres alone, 

 although it is probable that the higher centres in the cord and upper parts of 

 the cerebro-spinal axis play an important secondary part in its conditioning. 

 The movements may also occur after the destruction of the lower part of the 

 spinal cord which contains the centres for the extensors of the ankle. But 

 this does not necessarily mean that they would continue if all the extensor 

 centres could be removed from the lumbar spinal cord. In this experiment 

 there yet remained the extensor centres for the thigh. The movements may 

 finally occur after the removal of a great part of one lateral half of the 

 lumbar spinal cord. This all speaks for the independence of the lumbar centres. 



It is true that in these experiments the movements were not observed after 

 the de-afferentation of a hind limb in that limb. It must, however, be 

 remembered that the movements of progression after division of the spinal 

 cord have appeared in these circumstances, and so have the similar move- 

 ments of rhythmic rebound. Perhaps the afferent proprioceptive impulses, 

 which are almost certainly reinforcing impulses and not essential to the act 

 in the phenomenon of narcosis progression, play a greater part in the 

 depressed state of the lumbar centres which is conditioned by the chemical 

 narcotic. If so, it is of interest that the motor paralysis of a limb 

 (accompanied by its de-afferentation, either actual or virtual) has little 

 effect upon the movements of progression narcosis which occur in the other. 



