30 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



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, 

 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 



Fig. 11. Curve to show the effect of a 

 rise of temperature from 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. 



more and more depressed. The point of optimum effect is not iden- 

 tical for the different tissues of the same animal, much less so for 

 those of different animals, but the fact may be emphasized that in 

 no case do protoplasmic tissues withstand a very high temperature. 



