1898] PHYSIOLOGICAL ACTION OF PLASMOLYZING AGENTS 409 
tions and left for twenty-four hours. At the end of this time, 
the condition of the alge was examined into with greatest care, 
and the strongest concentration in which they survived was noted. 
This limit I have termed the boundary concentration, and regard 
it as a measure of the purely osmotic action capable of being sus- 
tained by Spirogyra. Having determined this point, I calculated, 
by the use of methods in no way involving the living cell, the 
concentrations of the solutions of other substances to be studied, 
which have an osmotic value equal to that of the experimental 
boundary concentration of cane sugar. The next step was to 
determine experimentally as just described, the boundary con- 
centration of each substance under study. 
If the alge survived in a concentration greater than that 
calculated from the value of cane sugar, the conclusion would 
necessarily follow that the substance in question was less harm- 
ful to the plants than sugar. This condition of things was in no 
case realized. If the alge first survived in the calculated con- 
centration, the action of the substance would be purely osmotic 
and equal to that of cane sugar. If the alge should first sur- 
Vive in a concentration more dilute than the calculated boundary 
concentration, the substance in question would be more harmful 
than sugar. 
In the realization of the third case, injury by one or both of two 
possible methods might be wrought; first, by a very rapid extrac- 
tion of water from the cell, violence might be done to the proto- 
plast through the lack of opportunity for the organism to accom- 
modate itself to the change; second, toxic action due to the 
chemical interference of the substance in solution with the mole- 
cules of living substance might also take place. In each special 
Case, it would be necessary to ascertain the kind of injury oper- 
ating. In doing this certain plain considerations should be 
borne in mind. Should Spirogyra be found to survive at a con- 
centration greater than that causing plasmolysis and less than 
the calculated boundary, the deleterious action would in great 
Probability be due to the osmotic properties of the solution, a 
Point again to be touched on in this paper. If, however, the 
