A ae Innervation of Antagomstic Muscles. 61 
phase (fig. 4, H). There seems for each intensity of stimulus a duration 
which best favours the occurrence and intensity of contraction-phase (fig. 4). 
The length of this period varies with the condition of the reflex preparation 
as well as with the intensity of the external stimulus. In fig. 4 the reflex 
preparation was of relatively low activity. The relation existing between the 
period of the stimulus and the development of contraction-phase recalls the 
observations of Bowditch and Warren* on the time-factor in the influence 
of precurrent stimuli from various sources on the amplitude of the knee-jerk ; 
also the relation observed by Yerkest between precurrent stimuli and a 
reflex elicitable from the frog. 
The contraction of the contraction-phase varies from a brief spasm (fig. 3) 
to a prolonged tetanus lasting many seconds (fig. 8, A and B). The con- 
ied 
traction may be of great amplitude and power. When intense it reaches its 
maximum with considerable speed (figs. 1 A, 6,7, 8, A and B). Its decline 
may be rapid (figs. 3, 4), but more usually is quite gradual (figs. 1, 2,7). Its 
decline is always, in my experience, more gradual than its ascent, and usually 
very greatly so (figs. 1, 2, 7). This is a point of difference between it and 
certain forms of strychnine reflex as exhibited by the same extensor muscles, 
and it constitutes a distinction of some importance for determining the 
relation of strychnine reflexes exhibited by these muscles to the normal after- 
phase of contraction which they also show.t 
* ‘Journ. of Physiology,’ vol. 11, p. 25, 1890. 
t Pfliiger’s ‘ Archiv,’ vol. 107, p. 207, 1905. 
{ Sherrington, ‘Journ. of Physiol.,’ vol. 36, p. 191, 1907. 
