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.

    35/950 (page 29)
    may be expressed by a curve such as is represented in Fig. 11, in which there are two maxima and two points at which irritability is lost. The second maximum indicates a fact of general physiological in¬ terest,—namely, that in all of the tissues of the body there is a certain high temperature at which optimum activity is exhibited, and if the temperature is raised beyond this point functional activity becomes more and more depressed. The point of optimum effect is not identi¬ cal for the different tissues of the same animal, much less so for those Fig. 11.—Curve to show the effect of a rise of temperature from 0° C. to 38° C. upon the height of contraction of frog's muscle. The first maximum at 9° C, the second at 28° C. Beyond 38° C. the muscle lost its irritability and went into rigor mortis. Fig. 12.—Curve to show the effect of a rise of temperature from 5° C. to 39° C. upon the duration of contraction of frog’s muscle. The relative dura¬ tions at the different temperatures are represented by the height of the cor¬ responding ordinates. of different animals, but the fact may be emphasized that in no case do protoplasmic tissues withstand a very high temperature. Functional activity is lost usually at 45° C. or below. The duration of the contraction shows usually in frog’s muscles a simple relation¬ ship to the changes of temperature. At low temperatures, 4 or 5° C., the contractions are enormously prolonged, particularly in the phase of relaxation; but as the temperature is raised the duration of the contractions diminishes, at first slowly, then rapidly, to a certain point—about 18° to 20° C., beyond which it remains more or less constant in spite of the changes in extent of shortening. The