210 
Mr. Home's Lecture 
of becoming shorter. We find, however, from observation, 
that when the extent of motion in a joint, or the distance be- 
tween the fixed points of the muscle, is accidentally altered, the 
muscle acquires a power of adapting its quantity of contrac- 
tion to the new circumstances which have taken place. 
This power in a muscle may be considered as a proof that 
the principle of contraction is independent of its particular or- 
ganization ; since it can undergo a complete change within 
itself, so that its fibres shall be shortened to one half of their 
original length, and still have the same contractile, power as 
when in its original state. 
The extent of this principle is well illustrated by the follow- 
ing case. A negro about thirty years of age, having had his 
arm broken above the elbow joint, the two portions of the os 
humeri were unfortunately not reduced into their places, but 
remained in the state they were left by the accident, till the 
callus or bony union had taken place ; so that when the man 
recovered, the injured bone, from the position of the fractured 
parts, was reduced almost one half of its length. By this cir- 
cumstance, the biceps flexor cubiti muscle, which bends the 
fore-ami, remained so much longer than the distance between 
its origin and insertion, that in the most contracted state it 
could scarcely bring itself into a straight line : this muscle, 
however, in time, as the arm recovered strength, adapted itself 
to the change of circumstances, by becoming as much shorter 
as the bone was diminished in length ; and by acquiring a new 
contraction in this shortened state, it was enabled to bend the 
fore-arm. 
Some years after this accident, the person died, and the cir- 
cumstances abovementioned being known, the parts were exa- 
