88 PHYSIOLOGY CHAP. 



By many authors muscular relaxation has been, and still is, 

 regarded as a simple effect of the cessation of contraction. This 

 is Fontana's theory that contraction throws the muscle into 

 elastic tension, so that when the contraction ceases the muscle 

 lengthens owing to its elasticity. But if contraction is not con- 

 trary to elasticity, it is plain that the muscle can only relax by a 

 chemical process which is opposed to that of contraction, owing 

 to which its form changes in a direction opposite to that of the 

 contraction phase. As early as 1874 \ve pointed out this logical 

 consequence of Weber's theory, and added further, " If the con- 

 traction, which is due to a fresh molecular arrangement to which 

 a shorter natural form of the muscle corresponds, be termed active, 

 we are equally justified in calling the elongation of the muscle 

 active, since it too is associated with a new molecular equilibrium 

 which accompanies the process of relaxation." Years after (1887) 

 Gaskell made the important discovery that electrical phenomena 

 accompany the inhibition of cardiac muscle by the vagus, and 

 disproved the hypothesis that the contraction of this muscle is 

 due to katabolic and its relaxation to anabolic chemical processes 

 (Vol. I. p. 332). More recently Fano (1901) extended this theory 

 (see p. 83), which in our opinion applies not merely to the heart, 

 but to all other muscular tissues. 



No special advance upon Weber's hypothesis has been made 

 by the physiologists who refer the transformation of the potential 

 chemical energy developed in muscle after excitation into 

 mechanical energy, to the direct effect of a special form of 

 chemical alteration. Pfliiger, in his famous memoir, 1 accepts 

 this theory of the origin of muscular energy without enlarging 

 on it. Fick 2 expresses himself more clearly, and states that " the 

 chemical forces of attraction must a pi*iori be more or less pre- 

 disposed in the direction of the mechanical action which is to 

 follow, and participate directly in the same." Chauveau 3 remarks 

 that " muscular contraction is a derivative of chemical work." 



This theory seems no less artificial than that of Weber. 

 According to Engelmann, moreover, it is irreconcilable with the 

 fact that during contraction an infinitely small portion of the 

 muscle substance is chemically active as compared with the total 

 mass of the muscle which remains passive. He points out that 

 the muscle contains 70-80 per cent water, and that the greater 

 part of the 20-30 per cent of the organic substances and minerals 

 of which it is composed take no chemical part in the process. Of 

 the carbo-hydrate group associated with the protein molecule, 

 which gives rise during excitation to the formation of C0 2 and 

 H 2 0, only small proportions are simultaneously affected. On 



1 Ueber die physiologische Verbrennung in den lebendic/en Organismen (1875). 



2 Atechanische Arbeit und Wdrmeentwicklung lei der 'Muskeltatigkeit (1882). 



3 Publications on Muscular Work and Energy (1891). 



