LIFE: ITS ORIGIN AND NATURE 13 
by “accretion,” or adding material to their own 
structure from the substance in which they 
are immersed, living substances grow by con¬ 
verting other substances into themselves by 
some process of “digestion.” Furthermore, cry¬ 
stals do not propagate, or reproduce themselves, 
in the true sense of the word. For these and 
other reasons, therefore, the idea that crystals 
are in any way analogous to living beings, has 
been largely given-up. 
Theoretically, some kind of spontaneous gen¬ 
eration, at one time or another in the world’s 
history, must have taken place, in order for life 
to become manifest at all; and yet science can 
find no proof of its occurring today. It has been 
suggested that, under differing chemical, ther¬ 
mal and atmospheric conditions—which may 
have existed upon this planet millions of years 
ago^-but which are today non-existent, 
some form of spontaneous generation may 
have been possible. However, it seems 
plausible to assume that any artificial condi¬ 
tions of the kind should be capable of being 
reproduced in the laboratory today. Yet, as be¬ 
fore stated, no adequate experimental proof 
exists that spontaneous generation ever takes 
place, in t«he true sense of the word. Since life 
seemingly could not have been spontaneously 
produced upon our planet, therefore, other 
theories were advanced in an attempt to account 
for its presence. 
There is the theory, for example, first ad¬ 
vanced by a French writer, Count Salles-Guyon, 
and defended by F. Cohn, H. Richter, Helmholtz 
and Lord Kelvin (being, in fact, made known 
