48 
Walter Stiles 
CHAPTER II 
THE SYSTEM INVOLVED 
The problem with which we are presented is then to discover the 
laws governing the penetration of substances into and through the 
living cell. It is obvious that it is of first importance to understand 
the system involved. Both from a chemical and physico-chemical 
point of view this is a very difficult matter. The essential of all 
living cells is protoplasm. The structure of this and its elementary 
properties have been described as among the most difficult problems 
with which the biologist has to deal (Bayliss, 1915). In its simplest 
form in Amoeba or Myxomycetes, the general body of the proto¬ 
plasm, that is, the cytoplasm apart from enclosed granules, appears 
as a clear viscous fluid, apparently structureless, capable of changing 
its form under the influence of external conditions, but remaining 
quite distinct from, and without any tendency to mix with, the 
medium external to it. 
It has been urged that protoplasm behaves as a liquid (Bayliss, 
1915). This is shown by (1) the fact that drops of water enclosed 
in it assume a spherical form, (2) Brownian movement 1 observed 
by R. Brown in 1827 (R. Brown, 1866), (3) the action of an electric 
shock under the influence of which, an amoeba, for instance, tends 
to form a sphere (Kuhne, 1864), (4) the behaviour of Myxomycetes 
(Lister, 1888). 
Under ordinary powers of the microscope certain parts of the 
protoplasm are visible as denser specialised organs of the cell: the 
nucleus, numerous small granules, and in plants the plastids. Apart 
from these, under the ultra-microscope (dark-ground illumination) 
the apparently homogeneous cytoplasm is observed not to be homo¬ 
geneous, but to contain a great number of minute particles (Gaidu¬ 
kov, 1906-1910; Mott, 1912; Price, 1914). This is the condition 
characteristic of colloidal solutions, and from ultra-microscopic 
observation it would seem reasonable to conclude that the cyto¬ 
plasm is frequently a colloidal liquid system or hydrosol. 
Cytoplasm then is not homogeneous, but consists of a denser 
phase dispersed through the watery dispersion medium. It thus 
1 Brownian movement of particles visible under the ordinary microscope 
cannot be observed in all cells or organisms (Seifriz, 1920). 
