THE MECHANISM OF LIFE 559 



the place of its origin. According to him the transformation of a 

 part of the heat into mechanical energy comes about by the short- 

 ening, as the result of being heated, of elements that are capable 

 of swelling. In the last assumption he relies upon the two facts, 

 that all positive, uniaxial, doubly-refracting substances, if capable 

 of swelling, upon doing so shorten in the direction of their optical 

 axis, and that bodies that are capable of swelling do so more when 

 they are heated. According to Engelmann's investigations there 

 exist in the anisotropic substance of muscle positive, uniaxial, 

 doubly-refracting elements ; and, as Engelmann likewise has shown, 

 in the contraction of muscle liquid substance passes over from the 

 isotropic, more liquid mass of the muscle-segment into the more 

 solid mass of the anisotropic disk, so that the latter increases in 

 volume. Engelmann supposes, therefore, that in excitation of 

 muscle the elements of the anisotropic muscle-substance, which he 

 terms " inotagmata," swell as a result of the heat derived from 

 chemical energy and shorten, so that a contraction of the muscle 

 results. Engelmann endeavours to make his idea especially clear 

 by an experiment, in which the contraction of muscle is imitated, 

 according to the thermodynamic principle, by the thermal swelling 

 and shortening of catgut. In a beaker filled with water there is 

 a stretched violin-string which is surrounded by a coil of wire and 

 is connected with a writing-lever. By the making of an electric 

 current the coil can be heated, so that heat is communicated to the 

 string. The result is that the string swells and shortens and per- 

 forms a certain amount of work by raising a weight. Upon the 

 breaking of the current and cooling of the coil the string is ex- 

 tended again. Through its ingenious simplicity this experiment 

 makes Engelmann's view extremely clear, and it is not to be 

 doubted that at lirst sight it prepossesses one in favour of the 

 thermodynamic theory. Nevertheless, there are many arguments 

 against the latter, and various weighty objections to it have been 

 brought forward, especially by Fick ('93, 1, 2). 



Unfortunately it is impossible to discuss here the various diffi- 

 culties that lie in the way of accepting Engelmann's theory. One 

 only may be mentioned briefly, because its consideration leads 

 to another view which, upon the basis of microscopic facts, is con- 

 nected with the chemical theories of muscle-contraction. It must 

 be demanded of a theory of muscle-contraction that its principle 

 shall hold good for the explanation not only of muscular movement, 

 but also of all other forms of contractile phenomena, i.e., for proto- 

 plasmic and ciliary movements also. " Since these are united by 

 close transitions with one another and with muscular movement, 

 the same explanatory principle must be able to find employment 

 in all." But the above theory does not wholly correspond to this 

 first and foremost requisite, which Engelmann himself puts forward. 

 It is not able, e.g., to explain the motile phenomena of amoeboid 



