78 OF VITAL MOTION. 



(b.) Of the organic force ^ not of a nervous cha- 

 racter^ as an agent in the movements of 

 voluntary muscles. 



A free supply of blood is essential to muscular 

 activity, and here also the freedom of the supply 

 would seem to be related to the state most opposed to 

 contraction. It has been shown by Mr. Bowman, 

 that the number of capillaries in muscular tissue cor- 

 responds very closely to the number of elementary 

 fibres, and " consequently the same amount of mus- 

 cular tissue, arranged as a large number of small 

 fibres, would be supplied with a larger absolute 

 number of capillaries than if arranged as a small 

 number of large fibres."* In the voluntary muscles, 

 therefore, where the fibres are much more delicate 

 and numerous than in the involuntary muscles, it 

 follows that the supply of blood must be greater in 

 the same ratio: and thus the system in which con- 

 traction is the most transient phenomenon, is found 

 to receive the greatest supply of blood. 



It is found, moreover, that voluntary contractions 

 become more prolonged and enduring as the activity 

 of the circulation in the muscles diminishes ; and thus 

 the manifestations of this form of irritability in 



* Todd and Bowman, op. cit. vol. i. p. 107. 



