284 



Mr. Graham Brown. 



[Apr. 11, 



The rate of the rhythm of these movements is about one to two beats per 

 second. Under normal circumstances it has been observed to be as slow as 

 0*6 beat per second, and as fast as 2-5 beats per second. In asphyxia tbe 

 beats become markedly faster (besides changing in other ways), and their 

 rate may then rise to one of 3 - 3 beats per second, or even more. 



The movements have been registered as they occurred in the isolated 

 muscles as well as in the intact hind limbs. They have then an appearance 

 exactly similar to that of the rhythmic movements seen in some of the other 

 types of progression examined. 



Another form of progression is that obtained on electric stimulation of the 

 cut surface of the spinal cord. This also closely resembles the other forms in 

 appearance and in rate of rhythm. If the strength of the exciting stimulus 

 be progressively increased the rhythmic reaction becomes less well marked 

 and finally disappears, the reaction becoming one of pure maintained 

 contraction. 



VI. Comparison of the Different Forms. 

 When one or more of these different forms of progression — in narcosis ; on 

 electrical stimulation of the spinal cord ; on rapid section of the lower thoracic 

 spinal cord ; in response to simple peripheral stimulation, either as a direct 

 response or as a " rebound " ; and in response to compounded peripheral 

 stimuli — occur in the same individual, the general appearances of the different 

 reactions are seen strikingly to resemble one another. Even peculiarities 

 present in one variety may be present in the other. Thus, in one instance, 

 the rhythmic rebounds ensuing on cessation of a reflex stimulus presented 

 the peculiarity that the " beats " were arranged in groups of two, the second 

 of which was smaller than the first. The " beats " of the progression move- 

 ments which were evoked subsequently on section of the spinal cord also 

 presented this peculiarity. 



VII. The Conditioning of Rhythmic Movements. 



These experiments seem to shew that rhythmic movements similar to 

 those of progression may be evoked on compounding two antagonistic 

 excitabilities, that is, two antagonistic states of excitement and inhibition in 

 each centre. They therefore seem to confirm the suggestion previously put 

 forward that this is the method of the determination of progression. 



In the first place the direct compounding of antagonistic excitations — seen 

 in the compounding of stimuli which evoke antagonistic reflexes — may in 

 certain cases produce the phenomenon. 



Secondly, the application of a simple stimulus may also do so. But in 



