120 REPORTS ON THE STATE OF SCIENCE.—1918. 
warm gelatin sol sets to a gel on cooling ; the first sign of change is 
that the ultra-microscopic droplets of the dispersed phase unite to 
form larger drops. If the solution is moderately concentrated, these 
drops unite together to form a network, but the watery phase is still 
continuous. On the other hand, if we begin with a solution of high 
concentration, the drops which first separate can be seen by their 
refraction to consist of the watery phase, so that the phase relations 
are reversed when compared with the former kind of gel. Thus the 
network may consist either of the more solid or of the more liquid 
phase. The properties vary accordingly. If the liquid phase is the 
continuous one, it can be pressed out by squeezing. [f the more solid 
constituent is the continuous phase, liquid cannot be pressed out 
except by a pressure sufficient to filter it through the more solid 
phase. 
The work of Clowes took its departure from an observation of 
Bancroft (1913) that a mixture of oil and water can be made into a 
permanent emulsion in two ways. One of these consists of drops of 
oil suspended in a continuous watery phase, as in cream ; the other 
is of drops of water suspended in a continuous phase of oil, as in 
outter. The former system is produced when sodinm soaps are used 
as emulsifying agents ; the latter if calcium soaps are used. Clowes 
(1916) showed that an emulsion of the former kind could be con- 
verted into one of the latter by shaking with a solution cf calcium 
chloride, while the latter could be changed into the former by 
shaking with sodium hydroxide. The changes may perhaps be 
realised hy the illustration of a set of islands joining together so as 
to be transformed into a series of lakes surrounded by land. Clowes 
describes further experiments which will be more appropriately 
discussed in the section dealing with the cell membrane. He shows 
how the nature of the system depends on the relative surface 
tension at the two sides of the soap film which is formed by adsorp- 
tion at the boundary surface between the two phases. It will be 
obvious that the physiological properties of the two kinds of system, 
the liquid and the gel, with the possibility of converting one into 
the other by phase reversal, must play an important part in cell life. 
That there are possibilities of the formation of membranes, 
doubtless of a gel nature, within the protoplasm of a cell is shown by 
the fact that different reactions can take place at the same time in 
different parts of the cell, notwithstanding the general liqnid 
nature of its contents. The view that the organization of the cell is 
of the nature of many minute factories, in which various operations 
are being carried on under the influence of the structure of the 
cell, is at the present time rapidly displacing that of “ giant” mole- 
cules with “ side-chains,’ which were supposed to be continually 
split off and exchanged for other chemical groups. The question is 
discussed in the British Association address of Prof. Hopkins 
(1913). Put in another way, limitation of the point of view to 
that of pure structural organic chemistry is showing itself to be 
incapable of explaining physiological reactions. Protoplasm is an 
extraordinarily complex heterogeneous system of numerous phases 
and components, continually changing their relations under the 
influence of electrolytes and other agents. 
