1906.] 



On Innervation of Antagonistic Muscles. 



493 



further increment produces great increase of response, the exaltation induced 

 by an intercurrent flexion-reflex need not be very extreme to give, neverthe- 

 less, a very apparent and great increase in the response. A not very 

 extreme superactivity induced in the internal condition of the arc might 

 suffice to give the external stimulus a value equivalent to a stimulus that 

 would produce a very much greater reflex response. 



In the homonymous flexion-reflex the increments of reflex response 

 ensuing from increments of intensity of stimulus follow, in my experience, 

 a more regular progressive increase (fig. 8) than in the crossed extension- 

 reflex. There is therefore with this flexion-reflex less chance of successive 

 spinal induction effecting an augmentation apparently so large as with the 

 extension-reflex. This also has to be remembered, therefore, in contrasting 

 the smaller effect observed in the induction of flexion by extension than of 

 extension by flexion in the hind limb. 



The linking together of the simpler reflexes which compose a usual reflex 

 cycle doubtless involves several processes ; it has attracted the attention of 

 observers from several points of view. Loeb* has illustrated how in regard to 

 segmental reflexes the effect of the reflex in one segment may be to transfer 

 the external stimulus to another segment where it in turn excites the 

 reflex of that segment, and so on further. In this way the reflex sequences, 

 which he terms " Ketten-reflexe," can be compounded. 



Another interesting connecting process welding simpler reflexes into more 

 composite is that discovered by v. Uexkiill.t He has shown that a piece of 

 musculature, under static conditions which make it of greater length, is more 

 prone to excitation through the nervous arcs than it is under conditions in 

 which its length is less. Thus, if we suppose a pair of muscles ; A and B, 

 which under equal activity retain the lever on which they antagonistically 

 operate in such a position that A is equal in length to B, and if we suppose 

 that a new position be given to the lever such that A is longer than B, the 

 neuro-muscular condition becomes altered so that A is more prone to be 

 excited through the nervous arcs than is B. If I represent rightly in this 

 way the principle arrived at by v. Uexklill, it will be seen that in some of the 

 experiments mentioned in this Note and in my previous ones, the con- 

 ditions resemble those in which v. Uexkull finds his principle at work. 



A third process, qualified to play a part in linking together simpler 

 reflexes so as to form from them reflex cycles of action, seems successive 

 spinal induction. It appears especially fitted to combine the successive 



* ' Vergleichende Gehirnphysiologie,' Leipzig, 1899, p. 96. 

 t ' Zeitschrift f . Biologie,' vol. 44. 



