430 Prof. Th. W. Engelmann. [Mar. 14 r 



The different parts played by "Thermal" and by " Chemical" Con- 

 traction in the different kinds of muscular contraction. But now th& 

 question may be raised : Is not p hysiological contraction due to tur~ 

 gescence by imbibition solely ? Do not we find a sufficient explana- 

 tion of all kinds of contraction in the change of the conditions of 

 imbibition, a change which must necessarily result from the chemical 

 action caused by the stimulus ? 



We have all the more reason to put this question, since we caa 

 prove, that in the physiological contraction of striated muscle-fibres 

 the doubly-refractive layers swell at the cost of the watery isotropic 

 layers. The microscopical examination of active living muscles and 

 of fixed waves of contraction has proved this fact beyond all question, 

 however much the opinions of different observers may diverge* 

 on other points. The swelling would, moreover, account for the 

 slight decrease of muscular volume observed in strong tetanic con- 

 traction. For, according to the experiments of Quincke, the imbi- 

 bition of water by organised bodies generally leads to a slight 

 condensation.* By this condensation further heat is developed, and 

 this heat might, by raising the temperature of the doubly-refractive 

 elements, be partially transformed into mechanical energy, and in. 

 this way contribute to the production of muscular force. 



Yet I cannot consider this explanation as sufficient for all the facts- 

 The same argument which in our eyes seems to dispose of the hypo- 

 thesis of the identity of chemical attraction and muscular force,, 

 viz., the infinitesimally small quantity of substance which is chemically 

 active during a simple contraction, seems to me to present a funda- 

 mental difficulty here also. It is hard to understand how through a 

 change in the material composition, effected at one infinitesimal point 

 within a soft watery substance, the whole mass should shorten and 

 thicken, unless there proceeds from, the centre of chemical activity a con- 

 siderable amount of Idnetic energy throughout the substance. 



The microscopic appearances which prove the turgescence of the 

 doubly-refractive refringent elements during a contraction, do not 

 exclude a direct thermo- dynamical effect. For the almost complete- 

 identity in the changes of form, and of optical and mechanical 

 properties, which the doubly refractive constituents of all histological 

 elements undergo during chemical and thermal contraction, seems 

 to bear out the hypothesis, that in the thermal shortening of doubly- 

 refractive elements, through the imbibition of watery fluid, we 

 get a shifting of solid and liquid substances analogous to that of 

 turgescence. In most of the microscopical phenomena, especially 

 the so-called fixed contraction waves, we have, moreover, to do 

 with a high degree of tetanic contraction, or even with rigor, in 



* In the thermal contraction of tendons and strings I have not yet been able to- 

 convince myself of a decrease in volume. 



