222 



HEAT AND PROTOPLASM 



[Cn. VIII 



unless otherwise stated. All readings not designated by the 

 sign are above the Centigrade point. The point of abso- 

 lute 0, to which we may have occasion to refer, is 273 C. 



2. THE EFFECT OF HEAT UPON THE GENERAL FUNC- 

 TIONS OF ORGANISMS 



Under this topic will be considered (1) the effect upon 

 metabolism, and (2) the effect upon movement and irritability. 



1. Effect of Heat upon Metabolism. Within certain limits 

 the relative increase of temperature leads to a relative increase 

 in the activity of the various metabolic processes. This is well 

 seen in those chemical changes which produce so-called phos- 

 phorescence. Many years ago MACAIRE ('21, p. 157) showed 

 for fireflies, and ARTAUD ('25, p. 372) for the organisms of the 

 sea, that light begins to appear shortly above 20, reaches its 

 maximum intensity at 40 in the fireflies and 35 in the water 

 organisms, and entirely disappears at 59 to 62 in the first 

 case, and 43 in the second. The temperature of these three 

 points lowest temperature of metabolic activity, temperature 

 of greatest activity, and highest temperature permitting of 

 activity may be called, respectively, the minimum, optimum, 

 and maximum temperatures for phosphorescence. 



The effect of temperature on metabolism is seen in the 

 absorption of oxygen by organisms. Thus VON WOLKOFF and 

 MAYER ('74) found that more oxygen is absorbed by seedlings, 

 as the temperature is increased, from to about 35 C. This 

 is shown in the following table. (From VINES, '86, p. 198.) 



