i GENERAL PHYSIOLOGY OF MUSCLE 91 



muscle in the formation and propagation of the contraction wave, 

 by which a part of the heat is transformed into mechanical work. 



To strengthen this ingenious hypothesis Engelmann devised 

 an experiment, in which the contraction of the muscle, owing to the 

 swelling and shortening of doubly refracting particles in the long 

 axis in accordance with the thermodynamic law, is imitated on 

 a violin string. He started from the fact that the property of 

 contracting in heat is not peculiar to muscle, but is inherent in 

 different degrees in all living tissues, and even in other organic 

 substances that contain a doubly refracting substance, e.g. a violin 

 string or specially prepared string of non-vulcanised indiarubber. 

 Engelmann's model is shown in Fig. 62. He proved that under 

 definite experimental conditions a moistened violin string, thrown 

 into tension by a weight, thickens and shortens and does a certain 

 amount of work when heated by a coil of platinum wire traversed 

 by an electrical current, and lengthens again on cooling when 

 the current is interrupted. In this experiment the violin string 

 which contains the doubly refracting substance represents the 

 inotagma or anisotropous element of the muscle; the vessel 

 filled with water the aqueous, isotropous muscle substance; the 

 platinum coil the thermogenic molecules; the closure of the 

 galvanic current the excitation of the inotagmata which gives 

 rise to contraction; the opening of the circuit the cessation of 

 excitation from which relaxation results. Nothing but the 

 transmission of excitation along the series of inotagmata which 

 causes the transmission of the contractile wave is absent in this 

 ingenious model. 



On recording the contractions and subsequent elongations of 

 the violin string on a revolving drum, Engelmann obtained 

 chordograms which resemble myograms to a surprising degree 

 (Fig. 63). This proves that they depend on a cyclic process as 

 after the warming which leads to shortening, the string lengthens 

 and returns (at least approximately) to its initial state on cooling. 



It may be objected to Engelmann's theory that it takes no 

 account of the electrical phenomena that occur in the muscle. 

 Before meeting this objection it is well to consider the different 

 hypotheses that have been put forward in favour of an electrical 

 origin of muscular energy. 



Prevost and Dumas, Meyer and Arnici compared the muscle, 

 owing to its striated structure, with a Volta's pile, which also 

 consists of discs. Voit, starting from the negative variation, 

 assumes that the muscle current diminishes in contraction, because 

 a part of the electricity developed in the muscle is transformed 

 into movement. Krause and Klihne compared the motor end- 

 plates to the electrical organs of Torpedo, and the action of nerve 

 on muscle to the discharge of a Leyden jar. According to du 

 Bois-Eeymond, on the contrary, it is the wave of negative 



