22 PHYSICS OF STREAMING 



to 45 C. may cause the viscosity to decrease to one -third its previous 

 value. 



In a cell of Nitella the times taken to cover a space of i mm. at 18 C., 

 27 C., and 45 C. were 54 sees., 38 sees., and 25 sees, respectively. These 

 velocities bear ratios of 1-3, 1-6, and 1-9, to the velocities deduced from the 

 velocity at ioC., by allowing for the viscosities of egg-albumin at ioC, 

 i8C., 27 C., and 45 C. Apparently, therefore, the velocity of streaming 

 increases in a greater ratio than the viscosity of egg-albumin or water 

 decreases. This is probably due to the increased respiratory activity at 

 the higher temperatures rendering more energy available, and hence 

 increasing the propulsive force, although only a small fraction of the total 

 energy of respiration is ever utilized in producing streaming movements. 



Similar ratios were given by Chara, Elodea, and Vallisneria, and they 

 suffice to show that the influence of temperature on viscosity is always 

 a very important factor in the kinetics of the cell, while the decrease in 

 viscosity due to a rise of temperature is probably mainly responsible for 

 the increase of velocity between o C. and 30 C. 



The fact that the plasma probably contains a variety of proteids does 

 not affect the general issue, since the temperatures selected for comparison 

 are all well beneath the coagulation temperature of even the most readily 

 coagulable proteids. Except in the case of solutions of KNO 3 , dilute 

 watery solutions all decrease in viscosity when heated, and the amounts of 

 decrease bear approximately corresponding ratios to those in the case 

 of water, so long as the solution is not over 10 per cent, strength. This 

 also applies to egg-albumin, as can be seen by reference to the pre- 

 ceding table. 



The increase in viscosity of egg-albumin occurs at too high a point 

 ( 6 3- 6 5 C.) to explain the retardation and ultimate cessation of streaming 

 at 5o-55 C., and its almost immediate stoppage at 55 C.-6o C. In this 

 connexion the coagulation temperatures of the chief varieties of coagulable 

 proteids are of interest, thus : 



Serum-albumin coagulates at from 70 C.-8o C. 

 Paraglobulin 70 -75 



Plant-albumin and egg-albumin ,, ,, 65 -70 



Myosinogen and fibrinogen ,, 55 -60 



Myosinogen, and probably fibrinogen also, do actually occur in plant 

 protoplasts, and hence there is every reason to suppose that the retardation 

 of streaming at high temperatures is due to slight partial coagulation 

 of these proteids, and possibly of allied ones also. The sudden stoppage 

 at 55 C.-6o C. is probably due to their complete coagulation. Various 

 signs of this are shown when the stoppage is not too rapid, as for example, 

 the jerkiness and irregular character of the movement before it ceases, the 



