THE PHENOMENON OF CONTRACTION. 



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 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. 



Zb 





6" io' IS' 20' 2S' S<r Ss' jr Sr *r 



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 



