THE CONCENTRATION EFFECT IN NITELLA

A method distinguishing between the concentration effect due to the cell wall and that due to the protoplasm is described: the importance of this lies in the fact that if the protoplasm shows a concentration effect one or both ions of the salt must tend to enter its outer surface. Studies on the concentration effect of KCl with living protoplasm of Nitella show that when P.D. is plotted as ordinates and the logarithm of concentration as abscissæ the graph is not the straight line demanded in the ideal case by theory but has less slope and is somewhat concave to the axis of the abscissæ. With a variety of salts the dilute solution is positive, which indicates that the cation has a greater mobility in the protoplasm than the anion or that the partition coefficient of the cation (A_c) increases faster than that of the anion (A_a) as the concentration increases. If the result depended on the partition coefficients we should say that when A_c ÷ A_a increases with concentration the dilute solution is positive. When A_c ÷ A_a decreases as the concentration increases the dilute solution is negative. In either case the increase in concentration may be accompanied by an increase or by a decrease in the relative amount of salt taken up. Theoretically therefore there need be no relation between the sign of the dilute solution and the relative amount of salt taken up with increasing concentration. Hypothetical diagrams of the electrical conditions in the cell are given. If we define the chemical effect as the P.D. observed in leading off at two points with equivalent concentrations of different salts we may say that the chemical effect of the protoplasm is very much greater than that of the cell wall.