Stiles and J 0rgensen. — Studies in Permeability . IV. 53 
Weight of tissue. 
Final value of 
conductivity. 
Total quantity 
of electrolytes 
in the system. 
E 
w' 
(W) 
(E) 
3*8 
258 
275 
72 
4 * 1 
3 °° 
322 
79 
5*8 
399 
440 
76 
9-4 
520 
605 
64 
14-74 
802 
1027 
70 
Thus the total exosmosis varies with the weight of tissue used. In the 
experiments to be described the weight of discs varied somewhat, and in 
some cases the deviation from the mean was as much as 5 per cent, of the 
mean value. Hence variations in the values for the final conductivity of the 
solutions are no doubt due to variations in the weight of tissue employed. 
It is, however, only the final value of electrolytic exudate which is affected ; 
slight variations in the weight of discs used will scarcely affect the quantity 
of exosmosis of electrolytes before the final condition is reached, and any 
differences in the earlier part of the process must be due to other causes. 
We have used potato in our experiments, as potato tubers yield a very 
uniform tissue, and individual variations are likely to be less than with most 
other plant organs. But the method can be used for almost any plant 
tissue. We ourselves have used discs of beetroot and other fleshy organs 
similar to those of potato, and we have also employed leaves of various 
kinds, as well as roots of living plants, and we have found the method to 
answer as well in these cases as with potato. 
In the cases described in this paper we have chiefly used concentrations 
of reagents which will produce irreversible changes in the permeability of 
the cell, i. e. lead to the death of the tissue. In these cases the morpho- 
logical structure of the tissue employed does not introduce much variation 
in the results, but if very low concentrations are used, such as would not for 
a long time lead to irreversible permeability changes, then the morpho- 
logical structure and chemical composition become of importance. This is 
easily observed by comparison of potato and carrot. With these reversible 
changes of permeability and their bearings on theories of permeability we 
hope to deal more in detail in a later paper. 
It is interesting to compare results obtained by this method with some 
others that have been employed in work on permeability. Two methods 
that have found favour earlier we have tried in this investigation. The first 
of these is the exosmosis of the red pigment from anthocyan-containing 
cells. For this purpose the root of the red beet has been much used in the 
past. As the cell membranes become more permeable the red-coloured sub- 
stance diffuses out, and the external solution becomes coloured with it. It 
is possible to follow the rate of exosmosis by measuring the colour intensity 
at different times by means of a colorimeter. By following both the increase 
in colour intensity of the external solution and its increase in conductivity 
