APPLICATIONS OF THE GRAPHIC METHOD. 
187 
during contraetion, and that all parts of the muscle-substance 
seem to share in the changes of form involved. 
THE ELASTICITY OF MUSCLE. 
In proportion as bodies tend to resume their original form 
when altered by mechanical force are they elastic, and the ex- 
tent to which they do this marks the limit of 
their elasticity. 
If a muscle (best one with bundles of fibers 
of about equal length and parallel arrange- 
ment) be stretched by a weight attached to 
one end, it will, on removal of the extending 
force, return to its original length; and if a 
series of weights which differ by a common 
increment be applied in succession and the 
degrees of extensions compared, as may be 
done by the graphic method, it will be appar- 
ent that the increase in the extension does not 
exactly correspond with the increment in the 
weight, but is proportionally less. With an 
inorganic body, as a watch-spring, this is not 
the case. 
Further, the recoil of the muscle after the 
removal of the weight is not perfect for all 
weights ; but within certain narrow limits 
this is the case, i. e., the elasticity of muscle, 
though slight (for it is easily over-extended), 
is perfect. When once a muscle is over-ex- 
tended, so weighted that it can not reach its 
original length almost at once, it is very slow 
to recover, which explains the well-known 
duration of the effects of sprains, no doubt 
owing to some profound molecular change 
associated with the stretching. 
The tracings below show at a glance the 
difference between the elasticity of muscle 
and of ordinary bodies. 
It isa curious fact that a muscle during 
the act of contraction is more extensible than 
Fie. 184,—Du_ Bois-Rey- 
mond’s apparatus for 
the study of elastic 
extension in muscle 
(after Rosenthal). 
The graduated rod 
attached to muscle is 
to be observed with 
a lens. 
when passive; a 
disadvantage from a purely physical point of view, but proba- 
bly a real advantage as tending to obviate sprain by prevent- 
ing too sudden’an application of the extending force. 
