ould be explicable by known
physico-chemical laws. Hence arose the scientific materialism which was
so widespread in the years following the general acceptance of Darwin's
theory. It was recognized, of course, that our knowledge of organic
chemistry was at the time entirely inadequate to place this belief upon
a proved scientific basis, but the expectation of proving it gave a
great impetus to the study of the physical and chemical phenomena of
life. This attempt was still further stimulated by the investigation of
the factors controlling development referred to in a preceding
paragraph, for it is evident that to a great extent at least these
factors are chemical and physical in nature. And concurrently, the great
advances in organic chemistry, resulting in the analysis and in many
cases in the artificial synthesis of substances previously regarded as
capable of production only in the tissues of living organisms, made
possible a much more thorough investigation of the chemical and physical
basis of vital phenomena. The result of this has been that to a quite
considerable extent the factors, hitherto mysterious, which control the
fertilization, division, and differentiation of the egg, the digestion
and absorption of food, the conduction of nervous impulses, and many of
the changes undergone in the normal or pathological functioning of the
organs and tissues, can be ascribed to chemical and physical causes
which are well known in the inorganic world.

As in other instances, however, some of which have been mentioned above,
the elucidation of the organism from this point of view has turned out
to be a much less simple process than the more sanguine of the early
investigators supposed. The more knowledge has progressed, the more
complex and intricate has even the simplest organism shown itself to be,
and although the mechanism of the parts is gradually becoming
understood, the fundamental mystery of life remains as elusive as ever.

The chief reason for this failure to penetrate appreciably nearer to the
central mystery of life appears to be the fact that an organism is
something more than the sum of its various parts and functions. In
tracing the behaviour of any one part or function, whether it be the
conduction of a nervous impulse, the supply of oxygen to the tissues by
the blood, or the transmission of inherited characters by the
germ-cells, we may be able to give a more or less complete
physico-chemical or mechanica