Page:Popular Science Monthly Volume 82.djvu/145

Rh 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 employed), i. e., with a marked increase in permeability. But if a calcium or other antitoxic salt is previously added to the solution, both the permeability-increase (as indicated by loss of pigment) and the toxic action 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 antitoxic effect. Professor Osterhout's experiments disclose similar conditions in plant cells; pure solutions of sodium chloride increase permeability—as shown by loss of turgor and increase of electrical conductivity—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 action of the salt solution. Cytolysis by substances like saponin may also be checked by neutral salts. It seems probable that the relations between 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 external 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 permeability—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 secretion, in the fertilization of the ovum, and probably in the general process of intake of food-materials by cells. The stimulation of irritable tissues is a process which exhibits a peculiarly intimate dependence on