THE INFLUENCE OF TEMPERATURE 



temperatures may partly be due to partial coagulation, and partly to passing 

 disturbances in the motor-mechanism. 



If raised only from 40 C. to 45 C. a similar transient acceleration 

 followed by a progressive retardation may be shown, without the power 

 of recovery being necessarily lost. When now rapidly cooled to 20 C. 

 a further retardation may ensue, followed usually after a few minutes to 

 an hour or so by a steady increase of velocity up to approximately 

 the previous initial velocity. If, however, the temperature falls rapidly to 

 from 35 C. to 38 C., and then very slowly to 20 C., the curious anomaly 

 may be seen that a falling temperature is accompanied by an increasing 

 velocity. 



The age of the cell is a potent factor in determining the optimal and 

 maximal temperatures for streaming, these being much lower in young cells 

 than in adult ones. Moreover, streaming is more easily stopped in young 

 cells without inflicting permanent injury. Thus in young cells of Nitella 

 and Chara, in which streaming has just commenced, the latter became slow 

 at 40 C. and ceased at 45 C., when raised not too rapidly to these tem- 

 peratures. At 20 C. it recommenced in from a quarter of an hour to 

 several hours afterwards. In the case of a slightly older cell, the velocity 

 of streaming began to decrease at 40 C., was slow at 45 C., and ceased at 

 48 C. to 50 C., recovery occurring if the exposure had not been unduly 

 prolonged. Finally, in adult medullary or internodal cells streaming was 

 usually very slow at 50 C., almost ceased at 60 C., and completely 

 at 65 C., no recovery occurring if the cell was longer than five minutes 

 above 60 C. Indeed, five minutes' exposure to 60 C. suffices usually to 

 affect the cell fatally, without streaming entirely ceasing during the actual 

 exposure. 



At each temperature a velocity of streaming is assumed which may or 

 may not alter on prolonged exposure. Above 30 C. the immediate velocity is, 

 in the absence of a retarding shock-effect, always greater than that exhibited 

 a few hours or a few minutes afterwards. The first effect is to decrease 

 the viscosity of the moving layers and to increase the energy of respira- 

 tion, but before long the regulatory mechanism comes into play, and either 

 , less energy is employed in this manner than before or it is employed less 

 effectively. The viscosity of the protoplasm may also be increased by 



