80 
These curves were obtained by conducting the sound by means 
of a microphone to the string of the string galvanometer (Fig. 1 
and 2). 
Besides the movement of the string, S, the respiratory movement, 
A, and the movement of the upper eyelid, OU, were recorded. In 
these figures appears a distinct relation existing between the sound and 
the movement of the eyelid, whereas no constant relation between 
the sound and the respiratory movement may be detected. As will 
be exposed in the Archives Néerlandaises de Physiologie, the sound 
is caused probably by a simultaneous contraction of all extrinsic 
eyemuscles, which coincides with the going down of the upper 
eyelid. As may be seen in the figures the curve of the string was 
regular and distinct. The rate of the vibration was always about 
17 in one fifth second, that is about 85 per second. 
Apart from the fact that there is no agreement between the dif- 
ferent authors concerning the relation between the pitch of the 
muscle tone and the number of stimuli applied to the muscle nor 
concerning the number of stimuli necessary to produce complete 
tetanus and the number of impulses in voluntary contraction, in 
this case the number 85 agrees very well with the statements of 
Scuwarzkopr and Pürrer concerning the number of stimuli needed 
by bird’s muscle to go into tetanus and also with the values found 
by Weiss in the case of contraction by strychnine. 
