58 PHYSIOLOGY OF STREAMING MOVEMENTS 



of the sugar solution. The author is able to corroborate this observation, 

 although the difference of velocity is not always perceptible, especially in 

 short cells, while in long ones the slowing or quickening of streaming is 

 exhibited shortly after crossing the boundary line between the two fluids. 

 It can in such cases sometimes be clearly seen that the streaming layer is 

 thicker in the part immersed in sugar solution than in that in water, and this 

 although the sugar solution by withdrawing water from the protoplasm 

 would tend to diminish its volume. The explanation of the difference of 

 velocity is a very simple one, namely, the sugar solution withdraws water 

 from the protoplasm, increases its viscosity, and hence decreases the 

 velocity of streaming. As the stream enters the other half of the cell this 

 water returns, and the normal velocity is regained shortly after the cell has 

 crossed the boundary line. The net result is, therefore, an increase in the 

 time of a complete rotation. If the action were a stimulating one, as 

 Hormann supposes it to be, we should have an instance of a localized 

 stimulus which, acting upon an irritable and physiologically conducting 

 substance, either produces a localized effect without any transmission to 

 neighbouring equally irritable and physiologically connected parts, or which 

 is propagated to a very slight extent only in the direction of streaming. 

 This is, however, a physiological impossibility, since the stimulus when 

 first applied causes an almost simultaneous temporary stoppage over the 

 entire cell. 



The greatest difference of velocity observed amounted to one half of 

 the rate of the part in water, but was usually less pronounced. Now the 

 removal of not more than 17 to 18 per cent, of water from ordinary egg- 

 albumin nearly quadruples its viscosity, and since, other things being equal, 

 the velocity is inversely proportional to the viscosity, the observed difference 

 of velocity is just such as might be produced by the localized change in 

 the percentage of water, and its attendant alteration in viscosity, aided 

 possibly to a slight extent by localized alterations in the respiratory 

 activity. 



This action is, therefore, a direct physical one, although after a time 

 a stimulatory influence becomes perceptible in the form of temporary 

 stoppages of streaming in the part immersed in water. These might be 

 regarded as an attempt on the part of the cell to maintain the same 

 average velocity in the two halves, but frequently the stoppage extends 

 over the entire cell, owing either to a temporary derangement of the motor- 

 mechanism, or to disturbances in the metabolism on which the latter is 

 dependent, produced as the result of the continued exit and entry of water. 

 That these stoppages are not shock-stoppages, rendered possible by an 

 increase in the excitability of the cell after prolonged immersion'; is shown 

 by the fact that the excitability to other stimuli is diminished by such 

 treatment, and that ultimately the cells are killed. The sugar solution 



