1898] PH LOGICAL ACTION OF PLASMOLYZING AGENTS 4II 
per liter, and the most concentrated solution in which it can sur- 
vive is 34 gm. mol. Since cane sugar is assumed to have a 
purely osmotic action, we have in 34 gm. mol. of cane sugar per 
liter of water an osmotic quantity just small enough to permit 
life, and any other substance acting likewise in a purely osmotic 
manner will have as its boundary concentration, that concentra- 
tion which is equal in its osmotic action to a solution of cane 
sugar containing 34 gm. mol. per liter. 
We are able, assuming purely osmotic action, to calculate the 
concentration in which the algz will just survive. The boundary 
concentration of cane sugar, the osmotic value of cane sugar and 
that of the substance in question, being given, the boundary 
concentration would be found to be related to that for cane 
sugar inversely as the known osmotic values, according to the 
proportion 
Wie See ee 
in which S is the boundary solution of cane sugar; + the bound- 
ary solution of the substance; 0x the osmotic value of the sub- 
stance; and oS the osmotic value of cane sugar. 
Osmotic pressure is known to depend directly on the number 
of molecules or part molecules, ions, in the solution, and what- 
ever be the size of the molecules, an equal number will produce 
an equal osmotic pressure. Since the glycerin molecule under- 
goes no splitting into ions, like fractions of a gram molecule of 
cane sugar and of glycerin per liter of water should have the 
Same osmotic value. Hence, assuming physiological properties 
like those of cane sugar the theoretical boundary concentrations 
Should be the same, 34 gm. mol. per liter. It is seen, however, 
that Spirogyra is not able to survive under the conditions of the 
experiment, until a solution containing but one-half gm. mol. per 
liter is reached. It should be noted, however, that this concen- 
tration is stronger than that first causing plasmolysis. 
Why is glycerin more harmful than cane sugar? In spite of 
repeated experiments, no change of position could be determined 
for the boundary concentration. Since the Spirogyra still sur- 
Vives in a concentration stronger osmotically than the cell sap, 
