51 
the gastrocnemius in fig. 4 — as in all the other figures the lower 
one — somewhat resembles a sinusoidal line. The contraction- 
and relaxation-times are nearly equal, lasting about 0.08 second. 
At the highest point of the curve the m. tibialis abruptly begins to 
contract..The steep ascending part takes only 0.047 second, which 
is only about half the contraction time of the gastrocnemius. The - 
tibialis contraction continues and remains constant for 0.096 second, 
after which relaxation sets in, occupying 0.076 second. The whole 
cycle takes 0.21 second, the clonus being an extremely slow one, 
of only 4.7 vibrations per second. 
The difference in form and character of the gastrocnemius and 
tibialis curve is still more pronounced in fig. 5, in which the 
ascending period of the triceps curve lasts 0.077 second against 
0.021 second only for the ascending part of the tibialis anticus 
curve. The frequency in this case is 7.3 per second. These figures 
found for the time occupied in the ascending and descending 
periods in the individual contractions do not agree very well with 
those generally found in simple muscle twitebes. Yet the ascending 
part in tracings of simple twitches of the human tibialis anticus is 
always very small as compared with the relaxation time, whereas in 
curves of the triceps surae the difference is always much less 
noticeable. But may we compare a simple muscle twitch with a 
part of a clonus-curve? During a clonus the muscles are working 
under more or less abnormal conditions which do not resemble 
those under which records of ‘normal’ muscle twitches are 
generally taken. During the footclonus we generally bave to exer- 
cise a certain amount of pressure against the footsole. This means 
that, roughly considered, the gastrocnemius group are working 
against constant pressure, i.e. they contract isotonically. 
The contractions might even be considered to be as nearly as 
„ possible isotonical ones, if the action of the anterior muscles could 
be excluded. This is more or less the case with the simple foot- 
clonus in which the soleusgroup for practical purposes may be said 
to work isotonically, as the disturbing influence of the mass of the 
patient's foot and the examiner’s hand and arm’ will be hardly 
noticeable. The use of Errore Levi’s apparatus would bring us still 
a little nearer to perfect isotony. In cases of alternating footclonus 
we find that the passive tension on the triceps surae is rhythmically 
enhanced by the regularly occurring contractions of the tibialis 
group. Yet this influence of the tibialiscontractions on the triceps- 
curve is generally not very conspicuous, the gastrocnemius-group 
being many times stronger than the footextensor. Hence we may 
4* 
