Protoplasm to some Reagents . 
495 
osmotic pressure of the cell, as determined by the critical concentration of 
the plasmolysing salt, is very marked and readily followed. 
In 8 per cent. (1-4 M) ethyl alcohol 
the decrease in critical plasmolytic 
concentration is noticeable after one 
hour of treatment, although the amount 
of reduction is then slight, being 0-25 
per cent. After four hours of treat¬ 
ment the decrease in critical concen¬ 
tration is 0-75 per cent., after seven 
hours 1 per cent, (control 3 per cent., 
treated 2 per cent.). There is no 
further reduction, although the critical 
concentration remains low for some 
hours. 
With prolonged treatment in 8%)er 
cent, alcohol there is a gradual increase 
in critical concentration of plasmolysing 
salt, until, after one or two days, the 
osmotic value of the treated and still 
living cell has risen from the low value 
reached during the first few hours of 
treatment to that of the normal un¬ 
treated cell. 
If we wish to follow more ac¬ 
curately the change in osmotic pressure 
of a cell due to the effect of alcohol it 
is best done with a solution of still 
lower percentage. This has been done 
for 3 per cent. (0-5 M) ethyl alcohol. 
The values are given in the form of a 
curve in Fig. 4. The abscissae are 
days of treatment. The ordinates are 
critical plasmolytic concentrations. 
It will be noticed that there is no 
change in the critical concentration of 
salt (and therefore in the osmotic value 
of the cell) for eight hours. In eighteen 
hours the critical plasmolytic concen¬ 
tration has fallen to 2-2 per cent, (the 
Pays of treatment 
Fig. 4. The curve depicts the change 
in concentration of potassium nitrate necessary 
to plasmolyse cells treated in 3 per cent, ethyl 
alcohol. The ordinates are the critical plas¬ 
molytic concentrations, 3 per cent, being that 
ot the untreated leaf. The abscissae are days 
of treatment. Eight hours’ treatment in 3 per 
cent, ethyl alcohol are necessary before an 
appreciable reduction in critical concentration 
of potassium nitrate takes place. After 
eighteen hours’ treatment the lowest critical 
plasmolytic concentration (2.2 per cent.) is 
reached. After two days’ treatment the critical 
concentration has returned to the normal 
(3 per cent.). In two and a half days it 
has risen far above normal (to 4-5 per cent.), 
in four days to 5*5 per cent., and in five days 
to above io per cent. Since the osmotic 
pressure of the cell varies directly as the 
critical plasmolytic concentration, the curve 
indicates also the changes in osmotic value 
due to treatment in ethyl alcohol. 
normal being 3 per cent.). In twenty-four hours it has risen to 2-25 per 
cent. After two days of treatment the osmotic pressure of the treated 
leaves again equals that of the untreated. In two and a half days it 
K k 2 
