132 



Prof. J. A. Mac William. On the 



[Oct. 24, 



similarly treated ; the skeletal muscle went strongly into rigor mortis 

 after thawing. 



Again, it has been shown that freezing a contracted artery for some 

 time (e.g., 4 — 5 hours) completely and permanently abolishes the con- 

 traction. In rigid skeletal muscle the result is different ; in some cases 

 there is no perceptible diminution in the rigidity after thawing; in 

 other instances, the rigidity seems to be diminished but by no means 

 abolished. 



(4) The effect of heating a contracted artery is strikingly different 

 from what occurs when a skeletal muscle is treated in the same 

 manner. 



The contracted artery shows a characteristic relaxation at about 

 50° C, which may or may not be preceded by definite phases of 

 contraction and relaxation, as already described ; skeletal muscle in 

 rigor mortis shows no such relaxation. In its behaviour towards 

 changes in temperature the contracted artery shows an unmistakable 

 resemblance to what is seen in non-striped muscle that is unquestion- 

 ably alive, e.g., the muscle of the cat's bladder and the retractor penis 

 already referred to; there is an essential agreement in the main 

 features evident in each case — increased tonus on cooling, relaxation at 

 about 40°, followed by shortening, relaxation at 50 — 55° with final 

 abolition of tonus, &c. 



(5) When a strip of contracted artery is stretched by the successive 

 addition of equal increments of weight, its behaviour (as will be 

 presently described) is entirely different from that of a rigid skeletal 

 muscle. A strip of relaxed artery, on the other hand, gives results 

 essentially similar in their general character to those yielded by 

 skeletal muscle. 



(6) When a contracted artery is distended by internal pressure, it 

 can often completely recover its original volume in the contracted state 

 when the distending force is removed; indeed, in some instances it 

 shows a subsequent increase of the original contraction. This is in 

 sharp contrast to rigid skeletal muscle which, as is well known, fails to 

 return to its former length when it has been stretched by the applica- 

 tion of weights. 



Elasticity of Strips of the Arterial and Venous Walls. 



Wertheim,* and all observers who have worked at the subject since 

 his time, have found that when strips of the arterial wall (aorta com- 

 monly used) are stretched by the successive addition of equal increments 

 of weight the amounts of extension produced do not remain constant, 

 but go on diminishing ; the coefficient of elasticity increases with 

 increased stretching. 



* ' Annales de Chimie et de Phys.,' 3e serie, toI. 21, pp. 385—414 (1847). 



