e just mentioned, it has been found
that the part of the protoplasm which is most active is always
electro-negative to the part which is less so; that is, the electric
current flows from the more active to the less active portion of the
protoplasm.

Many different explanations of the origin of the electric current which
develops when the protoplasm is stimulated into activity have been
suggested; but none of them have, as yet, any experimental confirmation.
The most that can be said is that whenever any stimulus excites the
protoplasm into activity, there is instantly developed in it an electrical
disturbance, which continues as long as the action is in progress. Recent
investigations, which have shown that there is a direct relation between
many of the vital processes of protoplasm and the ratio of the electrolytes
which it contains, particularly the ratio of sodium and potassium to
calcium, would seem to indicate that the development of the electrical
disturbance is a direct result of variations in the proportions of the
salts of these metals, either brought about by, or themselves causing,
changes in the permeability of the protoplasm, following the stimulus which
determines the nature of the activity which it is to undergo. But there is
as yet no indication concerning the mechanism by which this stimulation,
with its resultant electrical phenomena, is transmitted to the protoplasm
and accomplishes its characteristic effects.

ACIDITY OR ALKALINITY OF PROTOPLASM

The preceding sections of this chapter have dealt almost exclusively with
the physical properties of protoplasm; including the phenomena of solution,
ionization, surface boundary effects, and electrical disturbances, and
their probable effects upon the chemical reactions which constitute its
biological activities. It is necessary now to consider another phase of the
physical chemistry of protoplasm, namely, its chemical reaction, whether
acid, alkaline, or neutral, the effects of variation of this condition upon
the activity of the protoplasm, and the mechanism by which it tends to
preserve its own proper reaction in this respect.

The earlier methods of investigation of the chemical reaction of
protoplasm were all based upon its color reactions to various staining
agents. These sometimes led to erroneous conclusions, because of the
effects of the staining agent itself upon the tissue; some stains are
poisonous and result in the deat