388 Proceedings of Royal Society of Edinburgh. [sess. 
about ‘05 second, and of the gastrocnemius about *03 second (see 
Tracings Y. and VI.). 
(b) That when the tendon of the supinator longus was tapped 
contraction occurred in the biceps as well, and that the contraction 
of the biceps preceded that of the supinator longus. This could 
only occur as the result of some reflex in the cord. 
From these special conclusions the general one which I think 
may be drawn is, that these muscle and tendon jerks are really 
reflexes, but reflexes of a nature much more simple than the ordi- 
nary ones, in which sensory nerves, nerve centres, and motor nerves 
are concerned. Looking upon muscle, motor nerve, and central 
nerve cell as being composed alike of masses of irritable protoplasm, 
and remembering that the masses of irritable protoplasm which 
compose these can conduct equally well in either direction, we 
can suppose that the stimulus of the tap applied to the muscle, 
directly, or indirectly through its tendon, produces its contraction 
only after the impulse so generated has traversed through muscle 
and motor nerve fibre to nerve cell, and down again to muscle along 
the same nerve fibre. In this way, ceteris paribus, the longer the 
distance between a muscle and its nerve centre the longer will be 
the interval between the tap and the resulting contraction. This is, 
of course, borne out by these observations, the ankle jerk taking the 
longest and the wrist jerk the shortest time to occur, the knee jerk 
occupying an intermediate position. But the fact that contraction 
of the biceps occurred when the tendon of the supinator longus was 
tapped, and that the contraction of the former preceded that of the 
latter muscle, denotes that the impulse generated in muscle, motor 
nerve, and nerve cell, as the result of the tap, may be reflected from 
the nerve cell along other nerve fibres. We must conclude, how- 
ever, that for this reflex, as for a reflex along the same nerve fibre, 
a much shorter time is required than for one in which the afferent 
impulse travels along an ordinary sensory nerve. 
The phenomena of clonus bear out this view. Clonus may be 
regarded as being a series of jerks or contractions, each jerk or con- 
traction acting as the stimulus to the one which follows. The fact, 
then, that (as shown by the observations made on this patient, and 
as demonstrated by myself at greater length in a previous paper)* the 
* “ Clonus and Tendon Reflex Phenomena,” Edin. Med. Jour., Aug. 1880. 
