222 



HEAT AND PROTOPLASM 



[Ch. vni 



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 Oeganisms 



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 Macaiee ('21, p. 157) showed 

 for fireflies, and Aetaud ('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 69° to 62° in the first 

 case, and 48° 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 0° to about 35° C. This 

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



