1912.] Induced by Concurrent Excitation and Inhibition. 297 



events, they seem to be most evident when the excitatory content of the 

 ipsilateral stimulus is demonstrable 



Fig. 5.— Time-marker records in seconds. (Liverpool.) 



IV. Conclusion. 



Graham Brown has reported,* in the " de-afferented " low spinal prepara- 

 tion, regular movements of progression {i.e., alternate contraction and 

 relaxation in both extensors and flexors) occurring in a transition from 

 a predominantly flexed state to a predominantly extended state. He regards 

 this as a feature of " neural balance," and concludesf that rhythmic activity 

 is characteristic of concurrent flexor and extensor influences. Although, in 

 the cases I have described, the oscillations are usually far more rapid, and 

 never attain the regularity and orderly character of the walking reflex or the 

 scratch reflex studied by Graham Brown, yet the analogy is striking and 

 probably highly significant. Perhaps all are manifestations of a general 

 tendency of opposed influences in reflex centres, although themselves con- 

 tinuous, to produce rhythmic activity. If so, it is conceivable that some 

 conditions of intensity or time relations produce the regular movements of 

 progression by enabling the centres to fall into a rhythm natural to them, 

 whereas other conditions entering into my experiments just miss the natural 

 rhythm of the centres and produce a confused rhythm instead. 



The general conditions underlying the production of rhythmic activity 

 from a constant stimulus or source of energy are of fundamental interest. 

 No general law covers all cases, but the following conditions obtain in a 

 number of instances, notably that of the stream of air emerging from a tube 

 under water. A source of energy tends to produce an increasing force (A) 

 opposing a relatively constant force (B) which tends to keep the energy pent 



* ' Boy. Soc. Proc.,' B, vol. 84, p. 308. 

 t ' Quart. Journ. Exp. Physiol.,' vol. 4, pp. 393—394. 

 VOL. LXXXV. — B. X 



