MEMBRANES AND CELL-PROCESSES 141 



soluble yellow pigment. The eggs or larvae die rapidly in pure isotonic 

 solutions of sodium salts, and this toxic action is associated with a loss 

 of pigment (more or less rapid according to the particular salt em- 

 ployed), i. e., with a marked increase in permeability. But if a calcium 

 or other antitoxic salt is previously added to the solution, both the per- 

 meability-increase (as indicated by loss of pigment) and the toxic ac- 

 tion are prevented or greatly retarded. Apparently, a pronounced and 

 persistent permeability-increasing action is equivalent to a toxic action ; 

 the calcium' prevents or retards this destructive action of the sodium 

 salt on the plasma-membrane, and hence has an anti-cytolytic or anti- 

 toxic effect. Professor Osterhout's experiments disclose similar con- 

 ditions in plant cells ; pure solutions of sodium chloride increase perme- 

 ability — as shown by loss of turgor and increase of electrical conductiv- 

 ity — and have a well-marked toxic action ; both of these effects may be 

 prevented by adding a little calcium to the solution. In all of these 

 cases the antitoxic action apparently consists in protecting the surface- 

 film against the permeability-increasing action of the pure sodium salt 

 solution. I have found that not only salts of metals, like calcium and 

 magnesium, but also various lipoid-solvents or anesthetics may prevent 

 the cytolytic action of pure solutions of sodium salts in an essentially 

 similar manner. Evidently certain changes in the state of the lipoids 

 in the membrane render the latter more resistant to the disruptive ac- 

 tion of the salt solution. Cytolysis by substances like saponin may also 

 be checked by neutral salts. It seems probable that the relations be- 

 tween bacterial cytolysins and anti-cytolysins are of the same essential 

 nature. The theory of antagonistic salt-actions may thus become of 

 the greatest importance as a guiding principle in practical therapeutics. 

 Such surface-actions as those just described constitute only one form of 

 toxic action, but they are among the most important because of the ex- 

 ternal position of the plasma-membrane in the cell and its consequent 

 direct accessibility to modification by changes in the surroundings. 



The integrity of the plasma-membrane thus appears to be essential 

 to the normal living cell. Injury to this membrane thus means toxic 

 action: prevention of this injury is antitoxic action; restoration of the 

 normal permeability after injury is therapeutic action. But the plasma- 

 membrane does not play only the purely passive role so far indicated. 

 It is intimately concerned in many active cell-processes; and there is 

 evidence that many of the distinctive energy-manifestations of the cell 

 are determined or controlled by changes — largely changes of permeabil- 

 ity — which have their seat in this structure. This appears to be true of 

 many forms of cell-movement, of cell-division, and of the stimulation- 

 process in general. Permeability-changes are also concerned in secre- 

 tion, in the fertilization of the ovum, and probably in the general proc- 

 ess of intake of food-materials by cells. The stimulation of irritable 

 tissues is a process which exhibits a peculiarly intimate dependence on 



