1912.] Rhythmic Activity of the Nervous System. 



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crossed primary centres. It will be observed that in this scheme no 

 explanation of the nature of the inhibitory process is given. 



Summary. 



1. In the case of simple peripheral stimulation the reflex response is 

 sometimes of a rhythmic character. It then resembles the rhythmic move- 

 ments of progression which sometimes occur in the cat during the state 

 of narcosis. 



2. The rhythmic reaction occurs sometimes during the application of the 

 stimulus and sometimes at its cessation as a rhythmic rebound. 



3. In the low spinal preparation the rhythmic reaction during stimulation 

 is rare. It is seen almost alone after the production of an artificial state of 

 maintained extension by mechanical stimulation of the spinal cord, and in 

 response to flexion-producing stimuli. Here it looks as if the reaction was 

 conditioned by the pitting against one another of two opposite activities. 



4. In the decerebrate preparation of the cat, rhythmic responses may 

 appear in reaction to flexion-producing stimuli. Here there is already, in the 

 decerebrate rigidity, a state of maintained extension. 



5. Both in the normal and in the de-afferented conditions of the low spinal 

 and decerebrate preparations the compounding of reflex stimuli, which, taken 

 singly, produce opposite reactions (flexion and extension), sometimes results in 

 a rhythmic reaction. The rhythmic movements may occur in both muscles, 

 and they are then reciprocally alternate. 



6. These rhythmic responses occur, as a rule, only within a restricted range 

 of strength of stimulation. If either stimulus be increased in strength, the 

 response during the compounding of the two stimuli ceases to be rhythmic. 



7. As already published, a rhythmic response is obtainable on rapid 

 division of the spinal cord. The movements of this are exactly similar to 

 the movements of progression. There is first a phase of maintained flexion, 

 and at the end a phase of maintained extension. These, on the whole, are 

 arrhythmic, and between them is a phase of " balance " in which the rhythmic 

 movements are most perfect. 



8. This previously led to the suggestion that the rhythmic phenomenon is 

 conditioned by a balance of two equal and opposite activities, that is to say, 

 by activities which produce in the same centre equal and opposite effects 

 (excitation and inhibition). In the experiments here given there seems to be 

 evidence that this suggestion is correct. 



9. The various rhythmic movements — during stimulation, rhythmic 

 rebound, on compounding equal and opposite stimuli, on rapid division of 

 the spinal cord, on unipolar electric stimulation of the cut surface of the 



