424 Prof. Th. W. Engelmann. [Mar. 14, 



in elasticity. It would be very strange if these shiftings did not 

 manifest themselves also in changes of the chemical processes, and 

 if these changes were not conformable to the purpose. 



Connected with the point we have just discussed is another fact, 

 viz., that the amount of shortening produced in our model by means 

 of a given rise of temperature, is the smaller the more the string 

 has already contracted. The maximum of force is, at all events, 

 displayed when the extension of the string is brought about by the 

 whole load being applied at once at the very beginning of the heating, 

 not after the string has already contracted with a smaller load. 



The very same thing, as Schwann's experiments showed many 

 years ago, holds good of muscle. On the hypothesis of chemical 

 attraction we should decidedly expect the reverse : viz., increase of 

 force with an increasing mutual approach of the combining molecules ; 

 so also in the same way on every hypothesis which pronounces 

 contraction to be caused by attractive powers increasing in inverse 

 ratio to the square of the distance. 



In the fact discovered by Schwann, Johannes Miiller thought he 

 had found a refutation of the old electro-dynamic hypothesis of 

 Prevost and Dumas, as well as a valid reason for assuming a 

 fundamental relation between the vital power of contraction and 

 physical elasticity. 



However, as Hermann has observed, we might in this case get 

 over the difficulty by supposing that between or in the length of the 

 parts attracting -each other, there are elastic layers opposing that 

 attraction with increasing force. It is evident that our view of the 

 matter does not require such an auxiliary hypothesis, because, 

 following Eduardi Weber, we regard muscular contraction as only 

 a special case of elastic shortening. 



A closer experimental comparison of the changes undergone, on the 

 one hand, by the elasticity of our string during thermal shortening, 

 and, on the other, by muscular elasticity during physiological 

 contraction, will teach us that, in each case, those changes are of 

 exactly the same kind. 



As regards striated muscles, it was Eduard Weber who, by his 

 classic researches, established that their extensibility increases during 

 contraction. The same is now proved to hold good of strings and 

 other organic doubly-refractive substances during thermal shortening. 



The curve of lengthening of all these objects inclines more sharply 

 towards the abscissa of the loads the higher the temperature. Both 

 curves converge and may finally even cross, i.e., a certain load being 

 exceeded we do not get contraction of our string, but lengthening 

 as the effect of heating. 



This circumstance explains the fact, sometimes observed by 

 E. Weber, that living, tired, heavily-loaded frogs' muscles, lengthen 



