1908. ] Innervation of Antagonistic Muscles. 575 
contraction has fairly settled down to a grade somewhat less than half that 
acquired under the stimulation of the excitatory afferent nerve alone. The 
stimulation of the excitatory nerve is then withdrawn: marked further 
relaxation of the muscle immediately follows. Finally, the stimulation of the 
inhibitory afferent nerve is discontinued, and this is followed by a small and 
relatively sluggish rebound of contraction, such as formed the subject of a 
previous note (successive induction).* 
To assess the result of the combined stimulation in such an experiment as 
this it is necessary to compare the result with that obtained when, other 
conditions remaining unaltered, the sequence of the stimulations is made in 
the reverse order. This reversal was made and the record (fig. 4, A) obtained 
three minutes after the record, fig. 4, B. The concurrent stimulation of the 
antagonistic afferent nerves occurs under exactly similar circumstances as 
before, except that it breaks in on the reflex produced by the inhibitory 
component of the opposed nerves instead of by the excitatory. The height of 
the contraction under the combined stimulation is seen to be less in this case 
(fig. 4, A) than in the former (fig. 4, B). But in both cases the grade of 
contraction of the muscle is intermediate between that given by the excitatory 
afferent nerve singly and that given by the inhibitory afferent nerve singly. 
A further difference between the two records lies in the quicker subsidence 
of the contraction at the end of fig. 4, B than in fig. 4, A. This is due to the 
subsidence in the former being due to active inhibition. Whereas in 4, A the 
subsidence is due to cessation of excitation merely. 
The difference just noted in the degree of contraction under the combined 
stimulation, according as that stimulation succeeds an inhibitory or an 
excitatory reflex, is greater than usually occurs. This seems referable to the 
brevity of the combined stimulations in these examples. That it is so is 
indicated by experiments such as are illustrated by the records furnishing 
figs. 5, A and 5, B, In fig. 5, B the experiment opens with stimulation of the 
excitatory afferent nerve (contralateral popliteal, lower signal line) by 500 
Kronecker units. This stimulation gives immediate contraction of the muscle 
and the contraction has nearly reached its full height when, three seconds 
later, stimulation of the inhibitory afferent nerve (ipselateral peroneal, upper 
signal line) is commenced, stimulation of the excitatory afferent nerve con- 
tinuing as before. In this experiment the stimulus applied to the inhibitory 
afferent nerve is very weak, namely, 50 units on the Kronecker scale, threshold 
value of stimulus lying at about 35 on the scale. This weak stimulation of 
the inhibitory nerve nevertheless immediately makes itself visible on the 
myogram in a slight decrease in the height of the contraction of the muscle. The 
* ©Roy. Soc. Proc.,’ vols. 76 and 77, 1906. 
