1911.] Act of Progression in the Mammal. 



319 



the proprioceptive stimuli from the muscles themselves as the most impor- 

 tant, and the part which they play is essentially the regulative — not the 

 causative. 



This work has been done during the tenure of a Carnegie Fellowship, 

 and the expenses of the research have been defrayed by a grant from the 

 Carnegie Trust. 



Summary. 



1. By means of a stimulus (namely, section of the spinal cord) central in 

 application, although remote from the local centre, the act of progression 

 may be induced in muscles de-afferented by the cutting of their appropriate 

 posterior spinal roots. It occurs thus after all the muscles of both hind 

 limbs have been de-afferented, and all but the recording pair have been put 

 out of action by motor paralysis. 



2. The act of progression as exhibited by these muscles and thus induced 

 scarcely differs, if indeed it differs at all, from the act similarly induced 

 when the afferent arcs of the recording muscles have not been broken. 



3. In either case the reaction, as evidenced in movement at the ankle- 

 joint, shews three periods. In the first the record is characterised by a state 

 chiefly of maintained flexion. In the last there is a state characterised by 

 maintained extension. Intermediate between these there is a period of 

 " balance," in which the movements of progression are most perfect. 



4. The rhythhik sequence of the act of progression is cons, ■rpientlji determined 

 hy phasic changes innate in the local centres, and these phases are not essentially 

 caused by peripheral stimuli. 



5. Tlic proprioceptive stimuli which are generated by the contraction of 

 muscles taking part in the act (when the appropriate posterior spinal roots are 

 intact) play a regulating and not an intrinsic part in the act. Their chief 

 importance may be in the grading of the individual component movements to 

 the temporary exigencies of the environment. 



