540 
PHYSIOLOGY: W. O. FENN 
Figure 1 shows a set of Osterhout's electrical resistance curves for 
Laminaria, in which resistance is plotted against time. In his experi- 
ments resistance was used as a measure of permeability. From what 
has been said, it is to be expected that the Laminaria curves can be 
duplicated in alkaline gelatine which bears, of course, a negative charge.'* 
This is done in the following way. 
To a series of test tubes containing gelatine made alkaline (by adding 
enough NaOH to make the concentration 0.005M) is added NaCl, 
CaCl2, or mixtures of the two, in increasing concentrations. Each 
tube is then titrated with 95% alcohol until an opaque precipitate is 
produced. Figure 2 shows the results of such an experiment. In- 
spection of the curves shows that low concentrations of CaCl2 cause a 
decrease in the amount of alcohol needed for precipitation while higher 
concentrations cause an increase. NaCl causes only an increase. Mix- 
tures of NaCl and CaCl2 take intermediate positions. A comparison 
of these gelatine curves with the Laminaria curves in figure 1 shows a 
striking resemblance between the two. 
In spite of the difference in the methods of obtaining the curves in 
protoplasm and in gelatine, the two are comparable on the assumption, 
that the effect of time in the Laminaria experiments is to increase 
the concentrations of the salts in the cells of the tissue. We might 
then suppose that variations in the concentration of the salts pro- 
duced corresponding variations in the amount of a precipitate (e.g., 
at the plasma membrane) which offered a resistance to the passage of 
ions and so increased electrical resistance. This assumption would be 
rendered more probable if evidence were obtainable that the electrical 
conductivity of gelatine varies directly with the amount of alcohol 
required to produce precipitation. Some evidence on this point is 
already available. 
Samec^ working on a starch gel, measured the electrical conductivity 
and the alcohol precipitability simultaneously in lots of starch which 
had been heated for different lengths of time, and found that the two 
ran parallel to each other. Pauli® and his pupils state that the con- 
ductivity is a measure, other things being equal, of the number of elec- 
trically neutral particles present. Conductivity would therefore be 
least at an isoelectric point where, also, least alcohol is needed for 
precipitation. 
There are of course quantitative discrepancies in this analogy, but 
one could hardly expect gelatine to be as sensitive to electrolytes as 
protoplasm. Qualitatively, however, the resemblance between the two 
curves is remarkably close, even in the following details. 
