THE ENERGY EXPENDED IN A STREAMING CELL 27 



at i8C. That of the cell-sap will not be higher in the case of Nitella 

 than 0-025. 



Hence we may suppose that in each minute | -f ( T % x ) = 0-85 

 cubic mm. of liquid of viscosity 0-075 pass a given section. This equals 

 0-000,014 cubic cm. per i second. 



Now in the case of a liquid driven by pressure through a capillary 

 tube, if rj = the viscosity in dynes per sq. cm. (0-075) 5 



r = radius of capillary in cms. (0-04), and / = its length (2 cm.) ; 

 v = volume passed per second in c.c. (0-000,014) 

 p pressure in dynes per sq. cm. 



%r]vl 8x0-075x0-000.014x2 



Inen p = - 3 = - - - 2~ =2-1 dynes per sq. cm. 

 Trr 4 3-141,6x0-000,002,56 



Taking the density of the plasma as 1-2, 2 cubic centimetres would 

 weigh 2-4 grams. 



Hence per gram of plasma a force of = 0-875 dyne is required 



to impart a velocity of 2 mm. per minute. 



At this velocity a centimetre is covered in 5 minutes. Hence in i day 

 875 x 12 x 24 = 252 ergs of work are done. 



Taking the mechanical equivalent of heat as 4-18 x io 7 ergs. 



252 ergs correspond to -^ - ^ = 0-000,006,05 gram-calorie. 



But one gram of plant-fibrin yields 5,900 calories when burnt. 



Hence a minimum consumption of - ^ = g- gram of plant- 



fibrin or - g^ gram of albumin (heat eq. = 5,700) would be required per 



day, if the protoplast were a perfect machine. If glycerine, starch, cane 

 sugar, lactose, or dextrose J were consumed, about i| times as much would 

 be required. Hence to keep a gram of endoplasm of viscosity 0-075 

 moving with a velocity of 2 mm. per min. in a cell of the dimensions given 



requires only a theoretical consumption of yor - of a gram of cane 



sugar per annum, an amount so small as to be negligible. 



That the plasma has not a high viscosity is shown by the pronounced 

 action of gravity upon floating particles whose density differs but little 

 from that of the plasma. But even if the viscosity were as high as that 

 of a solution of egg-albumin containing 72 per cent, of water (0-29) the 

 theoretical consumption of energy would only be increased fourfold, and 

 would represent 0-00002 gram of sugar per gram of plasma per year. An 



1 One gram of glycerine produces 4, 200 calories ; starch and cellulose, 4,100 ; cane sugar, 4,000 ; 

 lactose, 3,900; dextrose, 3,700, when burnt into carbon dioxide and water. 



