1918] STILES & J@ORGENSEN—PERMEABILITY 529 
which is unproved, which at best must be incomplete, and from 
which indeed many workers now dissent (FISCHER 1, Moore, 
Roar, and WEBSTER 5, 6). When, therefore, OSTERHOUT says of 
us that ‘‘they regard the temperature coefficient found by them 
as the temperature coefficient of permeability to hydrogen ions,”’ 
he is completely misrepresenting our views on the matter. We 
never used the expression ‘‘ temperature coefficient of permeability ”’ 
for the reasons already mentioned, but if we had done so, we should 
certainly not have used the term permeability in the restricted 
sense in which OsTERHOUT appears to use it. 
We may point out that OsTERHOUT’s conclusion that we regard 
the temperature coefficient found by us as the “temperature 
coefficient of permeability” is based on the following assumptions: 
(1) that we “apparently reach the conclusion that ‘the substance 
with which the acid reacts’ is ‘presumably the plasma membrane or 
Some part of it’”’; (2) that we support the view of Pautt and 
Sztcs that the entrance of ions into the cell is due to the reversibil- 
ity of a reaction between ions and the plasma membrane; (3) the 
title of our paper ‘‘The effect of temperature on the permeability 
of plant cells to the hydrogen ion.” With regard to the first 
Statement, we neither apparently nor in reality reached that 
conclusion. What we actually said was that our results indicated 
“that the quantity of substance with which. the acid reacts, pre- 
sumably the plasma membrane, or some part of it, remains constant 
as it does not influence the rate of the reaction.’ This is quite a 
different statement. We said “‘ presumably the plasma membrane’”’ 
because it could not be assumed that it was the plasma membrane;? 
it might be any part of the cell. It is quite an immaterial point; 
our argument holds equally whether the action takes place in the 
limiting layer or elsewhere in the cell. 
Again, OsTtERHOUT’s second statement that we support the view 
of Pautt and Sztics is not founded on fact. We actually said, 
“this suggests that either the absorbing substance is present in such 
?The term “plasma membrane” is another of those semimystical expressions 
whose use does not help in the elucidation of scientific problems. We prefer to use this 
expression in the way that LEPESCHKIN uses it, simply as meaning that part of the 
cell where the permeability phenomena are taking place. Compare our recent remarks 
On this term (15). 
