243 
was the driving force in tlie evolution of all these forms and struc- 
tures ? 
In conclusion let us look at the third category of phenomena 
suggested at the beginning of my address — the phenomena of the 
actual functioning of the organism— of physiology. Here we meet 
with evidence indicating the use of chemical reactions. In many 
cases, however, the phenomena observed appear at first sight to be 
highly peculiar. Take for example certain phenomena of osmosis. 
Several cases of diffusion in the animal body have been considered as 
beyond physico-chemical explanation because they appear to be con- 
trary to what one observes in the laboratory or in the inorganic 
world. As Drieseli states, the fact has been quoted often that the 
migration of ions or compounds in the organism can happen quite 
contrary to all the laws of osmosis, from the less concentrated to the 
more concentrated side of a so-called membrane, Driesch continues 1 : — 
“There is no simple membrane in the organism, but a complicated 
organisation of an almost unknown character takes its place and 
nothing, indeed, is against the assumption that this organisation may 
include factors which actually drive ions or compounds to the side 
of higher concentration which indeed drive them by “doing work/’ 
if we like to speak in terms of energy; and these factors included in 
the organisation may very well be of a true physical or chemical 
nature.” 
It is quite evident fro.m this that Driesch looks upon physics and 
chemistry as explaining many processes that take place in the living 
organism, whilst at the same time considering them unable to account 
for all the phenomena of life. In the last few years physical 
chemistry has made progress in the elucidation of certain phenomena 
of osmosis, and it is interesting, perhaps, to note how an attempt has 
been made on physico-chemical lines to explain some of the pheno- 
mena met with in fishes . 2 In these animals the body fluids may pos- 
sess a saline concentration which is normally higher than that of the 
surrounding water in which the fish are living (fresh water teleosts) 
or may be much lower than that of the external medium (marine 
teleosts). This appears at first sight very extraordinary for there 
seems nothing* present to prevent simple osmosis taking place as it 
would if we separated a strong solution of salts from a weaker by a 
semi-permeable membrane. Experiments tend to show that the 
separating living membrane does not allow chlorine ions to pass 
through, although other experiments would indicate that it is to a 
certain extent permeable for them. The explanation of the problem 
is probably highly complicated. Donnan 3 has shown, however, that 
a membrane permeable to, say, Chlorine ions may actually separate 
two solutions with very different Chlorine concentrations. This 
1 Driesch. ibid p. 187. 
2 Dakin. Aquatic Animals ami tlieir environment. Intern. Revue d. ges. Hydro- 
trologie, 1912, 
3 Donnan. Theor. der’ Membrangleichgewichte. Leit. f* Elektrochemie. Bd. xvii. 
