Walter Stiles 
90 
3C 
the concentration gradient in the line of flow. Sziics assumes that 
the concentration gradient remains constant in each case throughout 
the time of the experiment, as the concentration of the external 
medium remains practically the same, and the dye is bound in the 
cell in some osmotically inactive form. Hence in the case of each 
concentration the quantity of dye absorbed will be proportional to 
the time and hence 
Q = kCt 
where Q is the total quantity of dye absorbed in the time t when the 
concentration of the dye in the external medium is C, and k is a 
constant depending on the coefflcient of diffusion and the dimensions 
of the cells, presumably assumed equal in all cases. 
Since Q is the same in all the experiments, it follows that if 
Fick’s law holds, Ct must be a constant. Experiments with neutral 
red showed that Fick’s law does not hold with regard to the absorption 
of this dye by Lemna minor. This is attributed to a complication 
arising through the adsorption of this dye by the cell wall. According 
to Ruhland (1908 a, b) this adsorption is prevented by the presence 
of hydroxyl-ions, and Szucs found that when neutral red was dissolved 
in 0*005 N sodium hydroxide, the product of the concentration and 
time required for the absorption of a definite quantity of dye was 
a constant both when Lemna and Spirogyra were used. 
The influence of concentration on the rate of intake of two 
alkaloids (piperidine and quinine) and a purine (caffeine) by two 
species of Spirogyra, was examined by Trondle (1920) by essentially 
the same method, the time being measured that was necessary for 
these substances in various concentrations to produce a visible 
precipitate in the cells. The same result was obtained as Sziics had 
found in the case of meth}d violet, namely, that the product of concen¬ 
tration and time is constant. This result supports the view that Fick’s 
law of diffusion is followed. This is in marked contrast with the 
results obtained by Trondle for the intake of salts, to which reference 
is made later in this chapter. 
The rate of absorption of different substances. Four sets of com¬ 
parative experiments were carried out by Stiles and Kidd to determine 
the differences in the rate of intake of a number of (1) chlorides, 
(2) sulphates, (3) nitrates, and (4) potassium salts. All the salts were 
employed in the same equivalent concentration, namely, 0*02 N, and 
the experiments were all conducted at the same temperature of 20° C. 
The relative absorption of the different salts after different times as 
