696 RALPH S. LILLIE 
is to be regarded as a consequence of increased surface permea- 
bility ;? hence the inference naturally follows that the critical 
change in the egg, to which membrane-formation and the initia- 
tion of cleavage are due, is a well-marked and rapid increase in 
the permeability of the plasma-membrane. 
The differences between the above salts are to be regarded as 
dependent on differences in the physico-chemical characteristics 
of their anions; the most effective salts, iodide and sulphocyanate, 
are those whose anions have greatest action in altering the state 
of aggregation of proteins and other negative colloids (including 
lipoids) in the direction of increased dispersion. The order of 
physiological activity thus corresponds to the order of relative 
action on colloids. The effect is therefore to be attributed to the 
action of the salt on the colloids of the plasma-membrane, whose 
permeability is thus altered at a rate and to a degree determined 
by the physico-chemical activity of the anion. 
A similar agreement between the order of relative physiological 
activity of neutral salts of alkali metals and the order of relative 
action on colloids has been observed in a variety of cases. From 
his experiments on the influence of isotonic solutions of these 
salts on the demarcation current of muscle Héber concludes that 
2 It appears out of the question to assume, as apparently some have done, that 
none of the pigment is free to diffuse within the cell, that it is all combined or ad- 
sorbed in solid granules or chromatophores. Granting that this is the case for 
part of the pigment, it is always necessary to assume the existence of an equi- 
librium between the adsorbed pigment and that in true solution and capable of 
diffusion. The homogeneous distribution of the pigment in Arbacia eggs in the 
space between the nuclear and plasma membranes is practically a proof of its free 
diffusibility; another and more cogent proof, is that it is liberated from the egg 
by any substance, irrespective of its chemical nature, that alters the surface pro- 
toplasm. That traces of saponin, mercury or silver salts, acid, alkali, as well as 
the above neutral salts, should all have the same effect, proves that a specifically 
chemical alteration is not the ground of the diffusion of the pigment to the exterior. 
The exit of pigment, besides being the most convenient index of a decided increase 
of permeability, has the advantage over indexes based on the use of foreign sub- 
stances, that a substance normally present in the cells is concerned. There is 
always the doubt, in estimating the permeability by the addition to the medium 
of a foreign substance like alkali, that the latter produces abnormal alterations in 
permeability and thus gains entrance. Final conclusions should be based on the 
use of several methods serving for mutual control. The possibility of selective 
permeability must also be taken into account. 
