1908. | Innervation of Antagonstic Muscles. 563 
and by so doing excites in it a proprioceptive reflex (the “shortening 
reaction”), reinforcing and subsequently maintaining its own contraction. 
The step has been taken, and both to the taking of it and to the resumption 
of it anew and to the ensuing maintenance of the standing posture, 
important contribution has been made by proprioceptive reflexes of the 
extensor muscle itself. 
EXPLANATION OF FIGURES. 
' Fia. 1.—Vasto-crureus preparation ; decerebrate cat. The base line shows the position 
of the leg when the knee is flexed. The first rise at S.r.! is due to lifting the leg 
below the knee into a less flexed position, and the horizontal line running to the 
right from that point shows the maintenance of the new posture by the tonus of 
vasto-crureus. The second ascent at S.r.2 is due to a second passive lift of the leg 
below the knee; the horizontal line running to the right shows the increased 
degree of extension of the knee now maintained by the tonus of vasto-crureus. At 
L.r.\ the knee was passively flexed nearly as far as the original degree of flexion, the 
horizontal line running to the right shows that the knee is now again maintained 
by the vasto-crureus in the new posture of flexion. The ascent of the line at S.7.3 is 
again due to a passive extension of the knee; the horizontal line running to the 
right from near the top of the ascent shows the maintenance of the new extended 
posture of knee by the tonus of vasto-crureus. The descent L.7.2 is due to a forced 
flexion of knee, and the horizontal line from its base indicates the maintenance of 
the new position of flexion by the tonus of vasto-crureus once more. The descent 
ZL.r.s marks a further forced flexion of the knee, bringing the knee to about the same 
degree of flexion as that from which it originally started ; the final horizontal line 
shows how the tonus of vasto-crureus maintains the limb once more at this level. 
Sir), S.r2, S.r.3: “shortening reactions” ; L.r.', L.r.?, L.r3 : “lengthening reactions.” 
During the execution of each passive movement the recording surface was not 
allowed to travel. 
Fig. 2.—Crossed reflexes produced in vasto-crureus by faradic excitation of the central 
end of the cut peroneal nerve of the opposite limb. Time marked above in 
seconds. Signal below marking the moment of application and the duration and 
frequency of repetition of the faradic stimulus. In A the record is from the 
left vasto-crureus, the afferent spinal roots through which pass the afferent fibres 
of the vasto-crureus nerve being intact ; in B the record is from the right 
vasto-crureus, the afferent spinal roots of its nerve having been severed 30 days 
previously. A and B are both from the same animal and experiment -and were 
taken within five minutes of each other. The tonic after-continuance of the 
reflex seen in A is absent from B. At Z.7. in A the movement of the recording 
surface was stopped and the extended knee was forcibly flexed and then released ; 
the recording surface was then allowed to proceed and the horizontal line of the 
tracing shows that the new length passively given to vasto-crureus was now 
maintained (“lengthening reaction”). If the “lengthening reaction” had not 
been made, the tonic after-continuance of the reflex would have gone on, probably 
for some minutes. Time marked above in seconds. 
The intensity and duration of the faradic stimulation was practically the same 
for both reflexes ;: a 100,000 ohms resistance was in the secondary circuit in both 
cases. 
In the reproduction of the records in the figures the reduction of size has been 
greater in A than in B; this difference can be judged from the time line. 
20 2 
