MUSCULAB CONTRACTION 



111 



MUSCULAR CONTRACTION 



Sarcolemma 



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 

 is suddenly raised by 

 passage of an electric 

 current, namely, a swell- 

 ing and consequent 

 shortening of the fiber 

 (Engelmann). In mus- 

 cle, the myofibrillaB 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 



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.") 



favor of such interpreta- 

 tion. The fibrillse short- 

 en and thicken in con- 

 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 



