The position occupied by the production of heat, in the chain of processes constituting a muscular contraction

THE processes which occur in the response of a muscle to an electric excitation can be classed under three headings:-(a) those occurring before, (b) those occurring during, (c) those occurring after, the actual muscle twitch. It is possible, a priori, that the heat prodtuction should take place either, (a) before, and in preparation for the mechanical response, or (b) during, and in intimate connexion with it, or (c) after, and in recovery fro>m the effects of the twitch, and in preparation for the next. For example, it is easy to suppose that (a) the heat is given out in some process whereby the tension of the muscle is suddenly increased, and that a twitch follows, consequent on this increase of tension. It may be, however, that (b) the heat is evolved in the actual process of