1097 
It is somewhat more difficult to understand the reflex-mechanism. 
We only know that the reflex is elicited by passive dorsal flexion 
of the foot. But then two things happen simultaneously : the extension- 
muscles of the foot are shortened and the triceps surae is stretched. 
Which of the two causes the reflex? I fail to see the possibility of 
choosing between the two on clinical grounds only. In the accident 
of a torn or cut Achillestendon, which is unlikely to occur in a 
healthy man, only a positive result would have any significance, as 
the reflex cannot invariably be elicited in healthy individuals. Some 
pathological arguments might perhaps be brought forward in support 
of the hypothesis, that the reflex is primarely caused not by the 
shortening of the muscle itself, but by the stretching of the antagonist. 
As regards the significance of the reflex we may assume that it 
is the same as that of more elementary reflexes, viz, a means of 
protecting the organism against exogene stimuli. The obvious fact is 
that the contraction assists the automatic tonus-mechanism in attaining 
as soon as possible the necessary muscular tension corresponding to 
the changed attitude. Hence we conclude that the reflex is a protect- 
ing mecharism against a total want of control over the position of 
the foot, if the foot is passively moved. 
I have already mentioned that in a few records a second con- 
traction of the tibialis anticus appeared immediately after the first 
(fig. 3). This may be caused either by a voluntary or by an invo- 
Fig. 3. 
Shortening reflex of the healthy leg of a hemiplegic 
patient. 
luntary impulse. In my experiments I have tried to exclude as much 
as possible any voluntary movements by impressing upon the subjects 
