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



during sncli a tetanus, a much greater part of the muscular substance 

 perhaps 1,000 times as much will be heated to such a degree 

 as is required for an obvious contraction of the inotagmata. But 

 even in this case the greater part of the whole substance will be only 

 moved passivelj. 



This holds good also, though in a less degree, of the single fibrils or 

 of the single sarcous elements, which, on account of their containing 

 doubly refractive inotagmata, we believe to be the sole producers of 

 shortening power. For it is beyond question that the sarcous elements 

 in toto are not subjected, even during the strongest tetanus, to a tem- 

 perature so high as is required by our hypothesis. Hence the specific 

 force of contraction of the individual doubly-refractive elements 

 must be comparatively much greater. We cannot properly calculate 

 how much greater the absolute force of a muscle would be if the 

 transverse section consisted of nothing but contractile inotagmata, 

 Tve can only assume that it would, in general, be many times as great. 



Can such very important mechanical powers as we are obliged to 

 assume in the inotagmata be developed through the thermal contraction 

 of doubly-refractive bodies ? Do we not, as Fick says, go beyond 

 the bounds of legitimate analogy in making such a supposition ? 



Of course nothing but the measurement of the forces developed by 

 lifeless doubly-refractive bodies under thermal contraction will 

 decide this question. I have made many of these measurements on 

 various objects, and I think the results furnish us with a refutation of 

 the objection. Strings, moist but not yet contracted through lying in 

 water, with a diameter of 0'7 mm., and loaded with 1 kilogramme, 

 lifted up the weight in a perceptible degree when rapidly heated up 

 to 130 C. ; that is to say, they exerted a force about twenty times at 

 least as great as the maximum force of a human muscle of the same 

 thickness. This is all the more striking, since in strings also it is not 

 the whole transverse section, but the sum of the sections of the 

 fibrillse, and even a part of every section only, which is the seat of 

 the power of shortening. 



Still greater forces may be exerted by strips of caoutchouc 

 rendered in a high degree doubly refractive by strong extension. 

 Even merely heating from 20 to 40 C. produced results sixty times 

 as great as the maximum afforded by human muscles of the same 

 transverse section. 



Hence we may sufficiently account for the greatest display of 

 force of which muscle is capable, without having to attribute to the 

 inotagmata higher elastic forces than we observe in highly extended 

 threads of caoutchouc of the same thickness, nay, without even 

 having to assume temperatures reaching the degree necessary for 

 the coagulation of albumin. 



Influence of Heat on the Dead Muscle Fibres. It is a pity that we 



