Conductance of Unicellular Organisms. 



285 



cent. Polarization capacity was compensated for by variable 

 condensers in parallel with the variable resistance. While most 

 of the studies here reported were made on the alga, Chlorella, 

 there is apparently no fundamental difference between this and 

 the other organisms. 



The difference between the conductance of the suspending 

 fluid and that of the suspension of cells is expressed in per cent, 

 of the former and called the net conductance. This will always 

 be negative in sign, because living cells are poor conductors of 

 electricity. Rather large variations in the net conductance are 

 produced by factors, such as irregular distribution of cells in the 

 suspension, which it is impracticable to eliminate and which may 

 affect the net conductance of any one sample by several per cent. 

 For this reason enough samples were used in each experiment to 

 make the error of the mean less than three per cent. 



It is possible to calculate the limits between which the ob- 

 served net conductance should fall, the relative conductance of 

 the cells themselves and their volume concentration being known. 



If r is the resistance of the suspending fluid and kr that of the 

 cells and n the concentration of the cells in volume per cent., 

 then the total resistance should lie between 



These formulas give curves convex to the axis of concentrations 

 when they are plotted against resistances as ordinates. But 

 when the cells form less than about 65 per cent, of the total volume 

 the observed curves are nearly linear, possibly because of varia- 

 tions in the relative extent to which the current lines are able to 

 evade the more highly resistant cell material. It is fortunate 

 that this is so, since in case the volume of cells varies during the 

 course of an experiment {e.g., because of osmotic changes) a linear 

 correction may be introduced. Different organisms and even 

 different lots of the same organism differ considerably in their 

 net conductance at any given concentration. 



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