MUSCULAR CONTRACTION 



111 



MUSCULAR CONTRACTION 



The physics and chemistry of muscle constituents are too inadequately 

 known to permit anything like a confident description of the mechanism 

 of contraction. It has been suggested that muscular contraction is essen- 

 tially a reversible coagulation process. The rapidity of the process seems 

 a fatal objection to this 

 explanation. A plaus- 

 ible interpretation fol- 

 lows the analogy afford- 

 ed by the action of cat- 

 gut suspended in water, 

 the temperature of which 

 suddenly raised by 



Sarcolemma 



is 



passage of ami electric 

 current, namely, a swell- 

 ing and consequent 

 shortening of the fiber 

 (Eiigelmann). In mus- 

 cle, the myofibrillse may 

 be conceived of as cor- 

 responding to the catgut 

 of the experiment, the 

 semifluid sarcoplasm to 

 the water, and the nerve 

 impulse to the electric 

 current. The rapidity 

 of muscular activity, 

 however, again seems a 

 difficulty. However, the 

 optical changes under- 

 gone by a contracting 

 muscle give evidence in 

 favor of such interpreta- 

 tion. The fibrillae short- 

 aiid thicken in con- 



Doyere's hillock 



en 



FIG. 126. LATERAL CONTRACTIVE WAVE OF CASSIDA 



EQUESTRIS. (After Rollet.) 



The formation of the contraction band is well seen, 

 at the left, as thick black lines. (From Szymonowicz- 

 MacCallum," Histology and Microscopic Anatomy.") 



traction, and there is a 



rearrangement of the optically different substances of the fiber; the dark 

 granules aggregate about the Z line, so that it seems to have disappeared 

 a change which involves also the disappearance of the original Q stripe. 

 We may be fairly certain that the explanation of muscular contraction must 

 be sought for in physical and chemical changes in the myofibril, it being 



