. Comparative physiology. Physiology, Comparative; Physiology, Comparative. MUSCULAR CONTRACTION 9 production and comparing the effects of stimulation upon heat- production in conditions promoting or impeding the recovery process. According to Hill's data three definite conclusions can be dra\vn. Firstly, when a muscle is excited directly or indirectly in oxygen by either a single shock or a short tetanus, the liberation of heat continues for some time after the mechanical response is over. Secondly, the amount of heat so liberated after mechanical response is over is, in oxygen, at least as g
. Comparative physiology. Physiology, Comparative; Physiology, Comparative. MUSCULAR CONTRACTION 9 production and comparing the effects of stimulation upon heat- production in conditions promoting or impeding the recovery process. According to Hill's data three definite conclusions can be dra\vn. Firstly, when a muscle is excited directly or indirectly in oxygen by either a single shock or a short tetanus, the liberation of heat continues for some time after the mechanical response is over. Secondly, the amount of heat so liberated after mechanical response is over is, in oxygen, at least as great as that evolved in the contraction and relaxation itself. But. Heat production in Ng Heat production in O.^ Fig. 2.—Scheme to illustrate modern work on muscular contraction. I. Latent period—concentration of ions at surface of excitation (elec- trical change). 2. Development of tension—associated with disappearance of glycogen and appearance of lactic acid. 3. Relaxation—lactic acid neutralised by buffer action of muscle proteins. 4. Recovery—lactate ions in part oxidised : some glycogen reappears, (a) Heat of formation of lactic acid from glycogen, {b) Heat of dissociation of muscle proteins. (c) Heat of combustion of part of lactic acid. thirdly, when the muscle is stimulated in nitrogen, there is hardly any heat-production after contraction is over, though the normal quantity is evolved when oxygen is again admitted. It seems therefore justifiable to infer that oxygen is used up, and " delayed " heat liberated, in that part of the recovery process which occurs after relaxation is complete. As we have already seen, this part of the recovery process is dependent on the presence of oxygen and cannot occur in pure Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hogben, Lanc
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