Stiles and J 0rgensen. — Studies in Permeability . I V. 
o*i am. isoamyl alcohol. 
Time. 
Conductivity. 
Colour. 
1.0 
40*8 
less than 0-05 
3 45 
128-8 
o-i 
19.15 
636*5 
1*0 
48.0 
750-0 
1-0 
0-08 m. isoamyl alcohol. 
Time. 
Conductivity . 
Colour. 
2.30 
55*2 
very slight 
19.30 
220-2 
0-2 
45.0 
578-0 
o -33 
0-04 m. isoamyl alcohol. 
Time. 
Conductivity . 
Colour. 
2.30 
23*5 
almost colourless. 
19.30 
I 20-0 
o-io 
43-30 
484-0 
0-14 
67.50 
719*5 
55 
It is clear that there is a rough parallelism between the exosmosis of 
electrolytes and of the sap pigment, but the measurement of the electrolytes 
can be accomplished much more easily and exactly than that of the 
pigment. 1 
Moreover, certain substances may react with the pigment and so 
change the colour, when colorimetric measurements would be rendered 
difficult or impossible. 
Incidentally it appears from a comparison of the results obtained with 
potato and beet that the latter contains somewhat more electrolytes than 
the potato. 
Another method which may be used depends upon the change of 
colour of the chlorophyll in leaves following on permeability changes in the 
cell which bring acids in contact with the chlorophyll. Chlorophyll when 
acted upon by weak acids gives derivatives of a yellowish or yellowish-green 
colour. The leaf of the Wood Sorrel ( Oxalis acetosella) is especially useful 
in this respect, as the colour change from a bright green to a bright yellow 
is particularly easily observed. 
The method has the disadvantage that it cannot be used kinetically. 
The only method of comparing the effects of different conditions is to note 
the time taken for the colour change to take place. It is, again, of very limited 
application as regards the tissue employed for experimentation. Further, 
any substance which neutralizes the acid in the cell-sap will prevent the 
colour change. 
1 Nevertheless, in the lower strengths of alcohol the pigment obviously diffuses out much less 
rapidly than the electrolytes. The question may arise here of differential permeability of the cell 
to different substances. With this question we may have occasion to deal later. 
