CHAP. VII.] CONTRACTILITY OF MUSCLE. 187 



vessels across them should determine the flexures to take place at 

 this or that particular point. When some fibres are straight and 

 others zigzag, and yet the ends of all equidistant, it is clear that the 

 straight ones are the short or contracted ; the zig-zag, the long or 

 relaxed. So, also, when a living muscle is laid bare in situ, the 

 air excites tremors and a zigzag appearance on its surface, by 

 the different fibres taking on non-simultaneous contractions. 



Schwann* contrived an apparatus by which he could estimate the , 

 varying force of contraction which a muscle could evince under 

 the same stimulus, (an electric shock of a given power applied to the 

 nerve), when its length was varied by its passive contractility 

 being balanced by different weights. He sought to discover whe- 

 ther the contractile force was increased as the contracting parts 

 approached each other more nearly. If he had found it so aug- 

 mented, there would have been some reason for connecting contrac- 

 tility with the other forces of attraction with which we are ac- 

 quainted, the power of which increases with the nearness of the 

 points attracted, in the ratio of the square of the distance. But the 

 result of several ingenious experiments were quite opposed to this 

 notion ; proving that, within certain limits, the power of a muscle to 

 contract under a stimulus is greater in proportion as it is less con- 

 tracted, and that it diminishes as the amount of contraction in- 

 creases. 



Considering, as we are perhaps entitled to do, that an equal mass 

 of each fibre, say one-third, was in contraction at any one instant 

 by each application of the stimulus, we may reduce the result of 

 these experiments to an estimate of the passive contractile power 

 under different amounts of stretching; for then the varying 

 amount of aggregate shortening under the same stimulus would 

 indicate the varying amount of resistance to elongation afforded by 

 the intermediate two-thirds to the same amount of active contractile 

 force in the one-third. 



It is clear, from that which precedes, that contractility is a pro- 

 perty residing in the sarcous tissue by virtue of its chemical constitu- 

 tion, and that it is capable of being called into action by other stimuli 

 besides the nervous. That it departs with life, is a proof that those 

 actions of waste and nutrition, concomitant with the flux of life, are 

 essential for its integrity. We know that contractility is exhausted 

 both by disuse of a muscle, and by over-use consequent on over- 

 stimulation ; and in no other way can these opposite causes act than 



* Mailer's Physiology, by Baly, p. 905. 



