1918] STILES & JORGENSEN—PERMEABILITY 533 
_ his discussion of our results, he would apparently apply conclusions 
derived from a brown alga immersed in a strong salt solution (about 
2), to potato tuber immersed in a dilute acid solution = : 
Such a method of argument seems to us illegitimate. It is not to 
be accepted as a first principle that the permeability of every tissue, 
and permeability in regard to every substance or ion, will follow 
the same law. Secondly, we should like to caution in regard to 
temperature coefficients. When the temperature coefficient of 
the absorption of water by one tissue is found to be about 1.3 and 
by another tissue 3.0, as we have found with carrot and potato 
respectively, it should make one hesitate to draw conclusions as 
to the nature of a reaction from the magnitude of its temperature 
coefficient. That the temperature coefficient of the absorption of 
hydrogen ions by potato tissue is about 2.2 suggests, as we said 
previously, that the absorption is controlled by a chemical action, 
but without further evidence it is not more than a suggestion. This 
is forthcoming from the shape of the time-absorption curve and the 
fact that the absorption of hydrogen ions continues long after the 
concentration of hydrogen ion inside the tissue would be greater 
than that outside if no chemical action took place. 2 
It must also not be forgotten that in cell problems we are dealing 
with a complex heterogeneous system, with probably a number of 
related and interdependent actions taking place, each one of which 
may have a different temperature coefficient. It would not be in 
any way surprising to obtain different coefficients for the same 
complex of processes with tissue that had had a different previous 
history, as we point out in a recent paper (16). 
In conclusion, we should like to enter a plea for definiteness of 
Statement and for the avoidance of semimystical expressions such 
as “permeability” or “plasma membrane’’ used in a quantita- 
tive and yet undefined sense. Above all, should be avoided the 
drawing of conclusions and the putting forward of theories on 
insufficient data. 
IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY 
LONDON 
