THE 
NEW PHYTOLOGIST 
Vol. XX, No. 2 June 30, 1921 
PERMEABILITY 
By WALTER STILES 
CHAPTER I 
INTRODUCTION 
I N the study of the living organism there presents itself a well 
marked group of problems arising from phenomena which can 
be included under the term “Permeability.” Every organism re¬ 
ceives from its environment in some form or another substances 
which enter into its body and which either as such, or after under¬ 
going physical and chemical change and working up into new com¬ 
binations, may be carried to every part of the organism. The 
problems concerned in this intake into the organism of substances 
from the surroundings, and their passage out from the cell into the 
external medium, and the translocation of substances from cell to 
cell in the body of the organism, may be spoken of broadly as 
problems of permeability. It must be admitted at the outset that 
the word permeability in biology is largely a cloak for ignorance. 
When the physical chemist speaks of the permeability of a mem¬ 
brane, he refers to the capacity of the membrane for allowing sub¬ 
stances to pass through it, and this is the logical and correct signifi¬ 
cance of the term. But this is not always what is meant when the 
physiologist speaks of the permeability of protoplasm or the per¬ 
meability of an organic cell. Sometimes he means the capacity of 
a substance to pass into or out from the cell, sometimes its capacity 
to pass through one particular part of the cell, as, for instance, the 
protoplasm, or the surface layer of it. The cell is a complex structure, 
and in the present state of our analysis it is rarely possible to localise 
the seat of any cellular phenomena exactly, although it must be one 
Phyt. XX. II. 
2 
