3] TEMPERATURE-LIMITS OF LIFE 231 



This shows that the muscle responds, and tends to return to 

 its uncontracted condition less quickly at a low than at a higher 

 temperature. In general, then, protoplasm is more responsive, 

 the closer we approach its optimum temperature. 



3. TEMPERATURE-LIMITS OF LIFE 



In the preceding sections we have seen that, as the tempera- 

 ture is raised above the optimum, or as it approaches C., 

 the vital activities begin to diminish. Finally, we meet with a 

 higher or a lower limit, at which all movement and the processes 

 of metabolism cease. This point may be called, in the case of 

 the higher limit, the maximum, and in the case of the lower 

 limit, the minimum. The maximum and the minimum are not 

 points of death, but merely of cessation of activity, lasting 

 while the temperature endures, but being replaced by renewed 

 activity when the temperature is shifted towards the optimum. 

 This quiescent, or latent, condition of the protoplasm near 

 the vital limits of temperature may be called temporary rigor 

 (German " Starre ") to distinguish it from death. Death occurs 

 at a very few degrees beyond temporary rigor. 



1. Temporary Rigor and Death at the Higher Limit of Tem- 

 perature, Maximum and Ultramaximum. (ENGELMANN, '79, 

 p. 358.)- -The occurrence, at a high temperature, of a con- 

 dition resembling death, except that the organism may revive 

 from it, seems first to have been noticed by P. DE CANDOLLE 

 ('06, p. 346). He found that a Sensitive plant, kept 11 hours 

 at 37 C., lost all sensibility to touch, and did not close with 

 the coming on of night. Maintained, during the following 

 day and night, at a temperature of about 20, it remained 

 insensitive during that period ; but on the succeeding night 

 it closed its leaves, and on the following day had regained its 

 sensitiveness to touch. Thus, the high temperature of 37 had 

 produced an immotile state which was not death, since it was 

 only temporary. It may be called the state of temporary heat- 

 rigor. 



The earliest record which I have found of a similar observa- 

 tion among animals is that of PICKFORD ('51). He states 

 that, at a high temperature, muscle went into a rigid con- 



