THE CHEMISTRY OF MUSCLE. 



69 



assumed that after stimulation the physical condition of the muscle 

 is changed and that the increased elastic attraction between the 

 particles gives it the form of the contracted muscle. According 

 to others (Fick), the mechanical contraction is a direct result of 

 an increased chemical affinity, while others (Miiller) find an ex- 

 planation in supposed electrical charges upon the doubly refractive 

 particles of the muscle in consequence of which there are developed 

 electrical attractions and repulsions at the different poles. The 

 most specific and comprehensible hypothesis advanced is that 

 formulated by Engelmann.* This author has shown that all con- 

 tractile tissues contain doubly 

 refractive particles, that in the 

 striped muscle fiber these par- 

 ticles are arranged in discs, 

 the dim bands, with the 

 singly refracting material form- 

 ing the light bands on either 

 side. During contraction it has 

 been shown that the material 

 of this latter structure is ab- 

 sorbed by the doubly refractive 

 substance. Engelmann has 

 shown, moreover, that dead 

 substances, which contain 

 doubly refractive particles, 

 such as catgut, when soaked 

 with water will shorten upon 

 heating and relax again upon 

 cooling. His explanation of 



f 



I 



Fig. 26. Engelmann's artificial muscle. 

 The artificial muscle is represented by the 

 catgut string, m. This is surrounded by a 

 coil of platinum wire, w, through which an 

 electrical current may be sent. The catgut 

 is attached to a lever, h, whose fulcrum is at 

 c. The catgut is immersed in a beaker of 

 water at 50 to 55 C., and "stimulated" 

 by the sudden increase in temperature caused 

 by the passage of a current through the coil. 

 (After Engelmann.) 



the mechanics of contraction in 

 brief is that the chemical 

 change brought about in the 

 muscle liberates heat, and that 

 the effect of this heat upon the 

 adjacent doubly refractive par- 

 ticles is to make them imbibe 

 the surrounding water. If we 



further suppose that these particles in the resting muscle are linear 

 or prismatic in shape, then upon imbibing water they will tend 

 to become spherical, causing thus a shortening in the long diameter 

 and an increase in the cross diameter. The muscle, in other words, 

 is an apparatus comparable, let us say, to a gas engine : each 

 stimulus, like a spark, causes the physiological oxidation of a portion 



* Ens;elmann, "Ueber den Ursprung der Muskelkraft," Leipzig, 1893; see 

 also " Pfluger's Archiv," 7, 155, 1873. 



