A textbook of physiology for medical students and physicians / by William H. Howell.

  • Howell, William H. (William Henry), 1860-1945.
Date:
[1905], ©1905
Catalogue details

Licence: Public Domain Mark

Credit: A textbook of physiology for medical students and physicians / by William H. Howell. Source: Wellcome Collection.

    34/950 (page 28)
    beyond which further increase of stimulus, other conditions remain¬ ing the same, causes no greater extent of shortening. Contrac¬ tions between the minimal and the maximal are designated as submaximal.* (See Fig. 9.) Effect of Temperature upon the Simple Contraction.—Varia¬ tions in temperature affect both the extent and the duration of the contraction. The relationship is, however, not a simple one in the case of the frog’s muscle upon which it has been studied most fre¬ quently. If we pay attention to the extent of the contraction alone it will be found that at a certain temperature, 0° C., or slightly below, the muscle loses its irritability entirely. As its temperature is raised a given stimulus, chosen of such a strength as to be maximal for the muscle at room temperatures, causes greater and greater Fig. 10.—Curve showing the effect of temperature. The temperatures at which the contractions were obtained are indicated on the figure. In this experiment a large resis¬ tance was introduced into the secondary circuit so that changes in the resistance of the muscle itself due to heating could not affect the strength of the stimulus. contractions up to a certain maximum, which is reached at about 5° to 9° C. As the temperature rises beyond this point the con¬ tractions decrease somewhat to a minimum that is reached at about 15° to 18° C. Beyond this the contractions again increase in extent to a second maximum at about 26° to 30° C., this maxi¬ mum being in some cases greater, and in others less than the first maximum. Beyond the second maximum the contractions again decrease rather rapidly as the temperature rises until at a certain temperature, 37° C., irritability is entirely lost (Fig. 10). If the tem¬ perature is raised somewhat beyond this latter point heat rigor makes its appearance, and the muscle may be considered as dead. The re¬ lationship between temperature and extent of contraction, therefore, * Fick, “ Untersuchungen fiber elektrische Nervenreizung,” Braun¬ schweig, 1864.