90 



PHYSIOLOGY 



CHAP. 



of a comparatively small number of molecules suffices to produce 

 contraction, which can only be explained on the assumption that 

 at the moment of oxidation they acquire a temperature so high 

 that their minute size and low number are perhaps the only reason 



why they do not appear 

 incandescent. The rise of 

 temperature in the total 

 mass of the muscle, even 

 granting that it only 

 amounts to O'OOl C. for 

 one contraction, is when we 

 consider the great specific 

 heat of the muscle sub- 

 stance i.e. the large 

 quantity of heat necessary 

 to raise its temperature 

 conceivable only on the 

 supposition that each heat- 

 producing molecule has at 

 its birth an enormous tem- 

 perature in comparison 

 with the immense mass of 

 substance able to conduct 

 and permeable to heat, by 

 which it is surrounded. 

 In this assumption it is 

 implicitly recognised that 

 the muscle presents to a 

 high degree the funda- 

 mental condition for the 

 conversion of heat into 

 mechanical work. This 

 conversion according to 

 Engelmann is effected by 

 the anisotropous substance 

 which forms the positive, 

 doubly refracting elements 

 with one axis parallel to 

 the direction of contraction 

 which he terms inotagmata. 

 He supposes that in mus- 

 cular excitation the inotag- 

 mata, warmed by the heat 



generated in the thermogenic molecules, swell up and shorten, 

 owing to imbibition of the more fluid isotropous substance that 

 surrounds them. This alternate swelling and shortening of the 

 inotagmata arranged in longitudinal series results in the whole 



FIG. 62. Engelmann's apparatus for imitating the con- 

 traction and relaxation of muscle on a violin string. 

 A string 5 cm. long soaked in water is fixed by its 

 lower end a to a rigid support 6, and connected above 

 by a strong silk thread to the short arm of the lever 

 H, which moves round the axis c. By means of the 

 movable weights d and d' the string can be thrown 

 into the desired tension, and the position of the lever 

 regulated by screw e. The string is surrounded by a 

 thin platinum wire /, which turns spirally round it, 

 and is soldered at the end to thick copper wires con- 

 nected with the poles of two Grove or Bunsen cells. 

 The string, platinum wire, and support are placed in 

 a wide low beaker filled with water, into which a 

 thermometer is introduced. When stretched by ai 

 weight of 25-50 grins, the string after a few minutes 

 ceases to expand, and the end of the lever remains 

 steady. If a current is then passed through the 

 spiral for a few seconds, the lever rises at once with 

 great rapidity, and on breaking the circuit it returns 

 almost to its original level, while the thermometer is 

 either stationary or shows a hardly appreciable rise 

 of temperature. 



