VOL. LXXXV.] PHILOSOPHICAL TRANSACTIONS. S'iQ 



increase the effect beyond the absolute contraction of the muscle. How these 

 different purposes are effected, I shall endeavour to explain. 



A muscle receives its nourishment from the blood, with which we find it more 

 abundantly supplied than most other 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 on the number of its fibres, and 

 most probably on 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 

 distinction 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 perhaps 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 exist- 

 ence 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 circumstances in which 

 the muscle is placed ; and the quantity of contraction appears to be limited by 

 the fibres having no power of becoming shorter. We find however, from ob- 

 servation, that when the extent of motion in a joint, or the distance between the 

 fixed points of the muscle, is accidentally altered, the muscle acquires a power of 

 adapting its quantity of contraction 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 organization ; 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 following case. A negro 

 about 30 years of age, having had his arm broken above the elbow joint, the 2 

 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 



VOL. XVII. 3 Y 



