and Bio-electrical Phenomena . 
675 
solution of salicylic acid from about 3 (which is roughly the pH of saturated 
salicylic acid) to at least 1 , since the electromotive force of the system 
saturated aqueous solu- oil intermediate con- saturated aqueous solu¬ 
tion of salicylic acid ductor, saturated with tion of salicylic acid 
without KC 1 salicylic acid containing KC 1 
is higher than 012 volt (compare table on page 147 and 148 of the book of 
the author), and since each 0-057 volt corresponds to a decrease of the pH 
value by one unit, as is well known. A decrease of pH from 3 to 1 would 
mean an increase of the H-ion concentration of about 1/1000 normal HC 1 
to 1/10 normal HC1, and yet such a concentration is brought about by the 
mere addition of KC 1 . Although the impossibility of this assumption is 
apparent, the author has performed a measurement of the pH of a saturated 
solution of salicylic acid (= 2, 8) which appeared not to be affected to more 
than o-i by the adding of 1/10 mol. KC 1 . 1 
No experimental evidence relating to salicylic acid, nor any quantitative 
calculation of the pH-values, is found in the criticism of Dr. Haynes. She 
asserts, however, that the author ‘ has altogether failed to substantiate his 
statement that salts rather than acids play the predominating role in the 
systems he investigates ’. ‘ A careful review of the experimental evidence 
shows the differences of potential which he obtains can be correlated with 
a difference of H-ion concentration whenever free acid is present in the oil and 
that the theory of salt action is derived from a misinterpretation of the 
complex chemical systems with which he [the author] deals.’ 
In connexion with these assertions another experimental conclusion of 
Macdonald may be quoted here : ‘ Solutions of NaOH, HC 1 , NaCl,or KC 1 
mainly affect the demonstrable value of the demarcation source according to 
their concentration.’ This shows the impossibility of potential differences 
correlated with the H-ion concentration being present in tissues, since pH 
is, of course, affected by HCl-concentrations in the opposite sense to that 
by NaOH-concentrations. 2 
No further details of the physio-chemical objections raised by Dr. 
Haynes need be discussed here, part of them being due to ascribing assump¬ 
tions to the author which he has never put forward, e. g. the assumption of 
1 In an article in the Biochem. Journal, xv. 440-61 (1921), Dr. Haynes describes measurements 
on the action of salts upon buffer solutions and finds that the adding of N/2-5 KC 1 decreases pH from 
6.88 to 6-7 (with a phosphate mixture instead of salicylic acid). It is obvious that in this case, also, 
the decrease of pH is far too small to account for such powerful electromotive effects as may be 
produced by the salt content. 
2 Macdonald’s statement is based on experiments with animal nerve. A similar experiment on 
plants was described by J. Loeb and the author (Biochem. Zeitschr., lxi. 15, 1912). It was found 
that the potential difference on the cuticle of a plant was not changed if HC 1 or NaOH was added 
while the salt content was kept constant. The large range of pH between 3 and 11 was found to be 
without any influence. It is very striking to compare these results with the statement cited above, 
that ‘ the potential difference can be correlated with a difference of II-ion concentration 
