244 
would occur if an anion R', and the undissociated salt NaR, were 
present on one side of a membrane impermeable to both, but per- 
meable to NaG which is present in solution on the other side. 
Owing to the presence of the non-dialysing substance NaR with the 
common ion Na the diffusion of the NaCI is hindered and in fact 
may be almost entirely prevented. Such mechanisms may be pre- 
sent in the living organism. There is no doubt, however, that the 
action of the membrane is different in aquatic animals immediately 
it is killed. But this could be put down to an alteration in its phy- 
sical or chemical condition. This is only one example of the appli- 
cation of physico-chemical methods to the study of the phenomena 
of life, and it .must be granted that these methods have elucidated 
much that once remained a mystery. We must not let ourselves be 
blinded by this success, nor must we fly to the opposite extreme and 
claim that the failure of our present knowledge to explain life 
phenomena means the presence of non-material factors. 
To sum up, our conclusions are largely negative in character. 
The general result appears to be that “We don't know.” Yet I 
think this result is not without value. The tacit acceptance of some 
explanation lias often kept back discovery for years. One could 
use no better illustration of this than Stahl’s fa.mous theory of 
phlogiston which ruled natural science with a rod of iron for prac- 
tically a hundred years. Curiously enough Stahl’s hypothesis was 
vitalistic. The time is not yet ripe for a tacit acceptance of En- 
telechy nor of any other similar non-material factor in the pheno- 
mena of life. It is just as certain that it is too soon to take as 
proved or even as probable the view that ordinary chemico-pliysical 
phenomena are responsible for all that we know as life. In fact, 
our discussion has lent support to the presence of some unknown 
factor which is as yet hidden from our ken. 
In the last few years a greater spirit of caution has been abroad 
— we are learning what complex pheno.mena we have to deal with in 
biological studies. The struggle to find simple theories has been car- 
ried too far. I might have said the struggle to find a theory, for 
scientists are often very intolerant, and it is sad to think of the 
wordy warfare that has raged on such problems as evolution, ac- 
quired characters, Mendelism, biometrics, and coral reefs and their 
origin. 
Biology has had a remarkable effect upon human thought and 
action since the time of Darwin — let us then tread carefully, by ex- 
periment and observation collecting our facts, until the time comes 
when Ave feel our results alloAV of certain deductions being made. 
I hen let us make them with a spirit of humility, being always pre- 
pared for newer knowdedge to prove or disprove our contentions. 
[ could not do better than conclude with the Avords used once by 
Professor D’Arcy Thompson : they meet our case so well : — 
“The reasons and the reasoning that contented a past genera- 
tion call for re-inquiry, and out of the old solutions neAv questions 
