28 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



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, 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 iiber elektrische Nervenreizung," Braun- 

 schweig, 1864. 



