54 
The difference was explained by considering the difference in force 
of the tibialis and the gastrocnemius contractions. In fig. 6 we have 
a clonus which is caused by the rhythmical contractions of the 
triceps surae and in which the tibialis anticus slightly partici- 
pates. In fig. 7 it is the tibialis group that entertains the clonic 
movement which is but slightly assisted by the gastrocnemius. 
We conclude this from the way in which in both cases the clonus 
was elicited. In the case of fig.6 the foot had to be forcibly pressed 
upwards. In the case of fig. 7 no pressure at all was necessary. 
I could start the clonus as well by a rapid passive extension of the 
foot as by a quick passive flexion. | may add here perhaps that in 
two patients I could elicit a clonus of the tibialis anticus alone, 
the triceps surae remaining completely at rest (fig. 8). With this 
record the pelotte for the gastrocnemius was placed on the middle 
and thickest part of gastrocnemius, in which I could not find the 
slightest trace of a contraction neither by inspection nor by palpation. 
The clonus could easily be started by a short passive plantar flexion 
of the foot. Both patients showing this clonus happened to suffer 
from incipient general paralysis. In one of them I also obtained an 
isolated clonus of the extensor hallucis longus. 
The occurrence of a real alternating clonus as described in this 
paper is rather rare. I think that hardly more than 2 or 3°/, of 
the cases of footclonus are such; we nearly always find a simple 
footelonus. My patients with alternating clonus suffered from multiple 
sclerosis, encephalomalacy or cerebrospinal syphilis; I also saw a 
few cases with apoplexia cerebri, braintumor, general paralysis, 
syringomyelia and atactic paraplegia. 1 do not think that I exaggerate 
in stating that every year I see about a dozen cases of alternating 
clonus against many hundreds of simple clonus. In complete medul- 
lary paraplegia I never saw alternating clonus. If we find it, it is 
always unilateral and invariably at the side of the lesser paralysis. 
The changes in the central nervous system were generally in both 
hemispheres and found to consist of multiple foci. No adequate 
explanation could be gathered from the localisation of the foci. 
I have tried to explain the alternating clonus, starting from some 
facts about cerebral innervation stated by SHERRINGTON. Stimulation 
of a cortical motor centre causes a contraction of a definite set of 
muscles as well as a relaxation of the antagonists. The centre 
performs a rather complicated function. About a few of these centres 
we even know that their function is still more complicated, 
probably on account of the action of secondary centres: we find this 
with the movements of walking, standing ete. Probably on walking 
