on Muscular Motion. 
209 
parts of the body. This supply is evidently intended for the 
support of its action, since it is proportioned to the exertions 
of the muscle ; and whenever a muscle is rendered incapable 
of acting, which frequently happens from the joints becoming 
stiff, the quantity of blood sent to it is very much diminished. 
The great vascularity of a muscle is, therefore, for the purpose 
of repairing the waste in the muscular fibres, occasioned by 
their action ; and without this support, the continuance of their 
contractions would be of short duration. 
The strength of a muscle must depend upon the number of 
its fibres, and most probably upon their size ; since in strong 
muscles the fibrous appearance is very obvious, while in very 
weak ones no such structure is visible to the eye. A distinc- 
tion of fibres has been considered as essential to the contraction 
of a muscle, and only those parts have been allowed to possess 
that power, in which fasciculi of fibres could be ascertained. 
But from the observations which have been made, it would per- 
haps be nearer the truth, to consider the circumstance of the 
fibres being distinct, as a proof of strength in a muscle, but 
not essential to the existence of muscular contraction. 
There is a power inherent in a complex muscle, by which it 
can increase or diminish the ordinary extent of its contraction ; 
this is very curious, and must arise from some change going 
on in the muscle itself, for which it is adapted by means of 
this very complicated organization. 
The usual quantity of contraction which takes place in the 
fibres of a complex muscle, in the different motions of the 
human body, is adapted in the nicest manner to the circum- 
stances in which the muscle is placed ; and the quantity of 
contraction appears to be limited by the fibres having no power 
mdccxcv. E e 
