494 Seifriz.—Observations on the Reaction of 
(i -6 M) is a critical point in the toxicity of ethyl alcohol on protoplasm. 
Above this concentration the protoplasm is killed in relatively few minutes. 
Below this concentration many hours are necessary to cause death. It is 
at about this concentration (1*5 M) that Stiles and Jorgensen ( 22 , p, 60) 
obtained a marked increase in the exosmosis of electrolytes from potato 
in solutions of ethyl alcohol. They found that the rise in electrical 
conductivity of the potato tissue after twenty-four hours of treatment 
in water was 79; in i-o M (6 per cent.) ethyl alcohol it was only slightly 
higher, no ; while in 1-5 M (8-| per cent.) alcohol it rose to 509 in twenty- 
four hours. 
Before death results in an alcohol-treated cell the protoplasm under¬ 
goes very pronounced changes in its physiological state, one of which is a 
change in permeability and a resulting change in osmotic pressure. This 
is determined by a reduction or an increase in critical concentration of 
the plasmolysing salt. 
Changes in Permeability and Osmotic Value. In this work the critical 
concentration of plasmolysing salt is that concentration of potassium nitrate 
which will slightly plasmolyse 50 per cent, of the cells of a leaf within 
half an hour. 
The critical plasmolytic concentration of untreated Elodea leaf cells 
varies considerably. It may be as low as 2 per cent. (0-3 M) or as high as 
5 per cent. (0-9 M) KN 0 3 . It is, therefore, highly important that the 
critical plasmolytic concentration of control leaves be determined in every 
experiment, and that these control leaves should come from the same 
general region of the same shoot of Elodea. Whenever possible the treated 
and untreated leaves should come from the same, or at least from neighbour¬ 
ing whorls. 
The concentration of potassium nitrate which is isosmotic with the 
contents of the average Elodea cell, i. e. the average critical plasmolytic 
concentration of untreated cells, is 3 per cent. (0-5 M), and unless otherwise 
stated this value will be employed for comparison. 
Cells placed for one quarter of an hour in 10 per cent. (1-7 M) ethyl 
alcohol show little change in their osmotic values. After half an hour of 
treatment there is a noticeable reduction in the critical concentration of the 
plasmolysing salt—from 3 per cent, of the control leaves to 2-8 per cent, of 
the treated leaves. Prolonged treatment still further lowers the osmotic 
value of the alcohol-treated'cells. The critical plasmolytic concentration 
of cells which have remained in 10 per cent, alcohol for three-quarters of an 
hour (and, of course, have remained alive) is 2-6 per cent, (the control still 
being 3 per cent.), and after one hour it is 2-5 per cent. 
The reduction in osmotic value of cells treated in 10 per cent, alcohol 
cannot be so readily determined owing to the rapidity with which the cells 
are killed. With lower percentages of alcohol the gradual decrease in the 
