1889-90.] Dr Hay craft on Voluntary Muscular Movement. 1 77 
are like a body of men pulling on a rope where perfect and pro- 
longed co-ordination is impossible. The proof of this is obtained 
by the use of very delicate levers attached to different parts 
(fasciculi) of the same muscle. Two levers attached in this way to 
a muscle always give slightly different curves, evidence of individu- 
ality being very apparent. Experiments were conducted both upon 
the human masseter muscle and upon the gastrocnemius of a frog, 
and in each case the curves obtained by the two levers correspond- 
ing in the main always differed in detail. 
It appears that the fibres running in a fasciculus are more co- 
ordinated together than those running in different fasciculi, and 
the following experiment shows that the nerve fibres passing from 
muscle fibres within a fasciculus run together towards the central 
nervous system in close relationship within the nerve trunk. 
Make a nerve muscle preparation from a frog, and apply a tiny 
drop of strong salt solution to one spot on the side of the sciatic 
nerve. After a minute or so the fibres within one fasciculus will 
twitch, then those within another, and so on until the whole muscle 
twitches. This is no doubt due to the gradual invasion of the 
nerve by the salt solution, the nerve fibres lying together, and 
therefore stimulated together, all passing to the same fasciculus. 
Inasmuch, therefore, as during a voluntary contraction fascicular 
movements are always going on, it may be that we have not to look 
any further for the cause of the muscle sound. This, as Helmholtz 
has shown in an ear resonance sound, would be bound to be set 
up by such movements, whether occurring aperiodically or at any 
slow period of their own. Kronecker, Schafer, Horsley, v. Kries, 
Landois, and others have figured tracings taken by levers and 
tambours of muscles contracting under the influence of the will. 
These tracings always show superimposed upon the main curve tiny, 
almost periodic, oscillations. These observers have considered the 
oscillations to indicate that the muscle as a whole is in incomplete 
tetanus during voluntary contraction, due to its receiving a series 
of nerve impulses breaking one after the other into it. The 
oscillations are due, however, to an entirely different cause. They 
are in reality the oscillations proper to the recording instrument 
which is kept oscillating by the aperiodic fascicular movements due 
to want of co-ordination. Granted such movements, which the 
VOL. XVII. 4/7/90 
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