28 



PHYSICS OF STREAMING 





actively respiring protoplast ma y, however, produce carbon dioxide at the 

 rate of over 10 grams per gram per year, which represents a consumption 



of 22 grams of sugar per annum. Hence 

 the amount of energy consumed in the 

 streaming movements within large cells 

 such as those of Chara, Nitella, &c., 

 forms an inappreciable fraction of that 

 produced by respiration, even if the 

 motor -mechanism is so imperfect as 

 to waste 99 per cent, of the energy 

 supplied. 



In cells with smaller radii, however, 

 the resistance to flow increases dispro- 

 portionately. The force in dynes per 

 sq. cm. required to drive the same 

 volume of liquid through capillaries of 

 the same length but with dissimilar radii 

 is inversely proportional to the 4th power 

 of the radius (n r 4 ). But if the velocity 

 of flow is constant, the volume passing 

 is directly proportional to the sectional 

 area (nr 2 }. Hence the force required 

 varies inversely as r*. 



Therefore if a force of -875 dyne 

 is necessary to move a gram of liquid 

 through a tube of o-i cm. diameter at 

 a velocity of 2 mm. per minute, a force 

 of 21-9 dynes will be necessary to drive 

 a gram of fluid through a tube o-oi cm. 

 diameter at a velocity of 0-4 mm. per 

 minute. In cells whose internal diameter 

 approaches o-oi cm. the average velocity 

 of the cell-sap and plasma is rarely more 

 than 04 mm. per minute. 

 At this velocity a centimetre is covered in 25 minutes. 



2I*Q X 12 X 2J. 



Hence per day = 1,251-8 ergs of work are done per gram 



o 

 of moving liquid. 



3 



F O 



FIG. 5. A. Diagram of streaming cell of Nitella, 

 major axis five, and minor axis ten times enlarged. 

 B. Section across the same magnified 50 diameters. 



This represents 



~~^ gram-calorie, or a consumption of 



4X 10 

 per day. 



4-i8xio 7 

 = -000,000,007,5 gram of cane sugar per gram of moving liquid 



