49 
In a few cases the tibialiscurve showed slight oscillations as in 
fig. 2. We easily find that these are not caused by real muscle 
Fig. 2. 
contractions, but by passive stretching of the muscle substance, the 
fascia and of the skin. The tibialis seems to thicken at exactly the 
same moment that the gastrocnemius contracts; this would mean 
jsochronous contraction in the antagonistic muscles, which a priori 
would seem to be improbable. But the experiment shows that also 
a very slow passive flexion of the foot stretches the skin, the fascia 
and even the tibialis muscle itself, so as to cause a pelotte placed 
on the muscle to rise a little, at least if the pelotte be placed too 
near the knee. If it were placed too far away from the knee, 
much farther than the thickest part of the muscle, I obtained curves 
as in fig, 3, in which the passive extension of the tibialis shows 
itself by a slight downward movement of the recording lever. 
Between these two positions we are always able to find an area 
where the receiving tambour may be placed so as not to be disturbed 
by passive movements of the foot, whereas contraction of the tibialis 
anticus are faithfully recorded. 
The placing of the receiving tambour on the gastrocnemius must 
also be done with the greatest care. 
At first I placed it laterally upon the muscle; afterwards I 
preferred to apply it exactly in the middle line, slightly above the 
thickest part of the muscle. With the pelotte against the lower part 
of the muscle or even against the tendon it is impossible to get 
satisfactory records. 
In contrast to numerous cases of simple footclonus we find every 
now and then a rare case in which inspection and palpation imme- 
diately show a participation of the anterior muscle group. Records 
of such cases of alternating clonus are shown in fig. 4—7. In all 
4 
Proceedings Royal Acad. Amsterdam. Vol. XXIV. 
