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INTRODUCTION. II 
origin of races, of languages, of the stars, etc. is a legitimate 
object of study, the origin of plants and animals is an in- 
quiry of an entirely different nature,—a subject about which 
man can learn nothing. Those who are continually referring. 
to the mysteriousness of Life as an objection to its study, 
seem to forget that the ultimate causes of all other phenom- 
ena, such as the falling of an apple, the combining of elements, 
the crystallization of a salt, etc., are equally mysterious. 
The forces by which these phenomena are brought about 
are studied in their effects; and the laws according to which 
these effects are produced belong to Astronomy, Chemistry, 
Crystallography. But of the cause or essence of gravitation 
we know nothing. We can only say that bodies attract one 
another according to a certain law. Equally unknown is the 
ultimate cause of crystallization. We can only say that in 
saline solutions, under favorable conditions, according to 
law, geometrical forms are produced. Compare now the 
growth of a crystal with that of a plant or an animal. Ifa 
seed be sown and it attract certain elements from the soil, 
a definite form, a plant, is produced; in the same way the 
chick results from the embryo attracting the material of its 
future body from the yelk. The laws governing the forces 
by which these effects are brought about, the phenomena 
of the growth of a plant or of an animal, are as legitimate 
objects of study as the growth of a crystal. The nature of 
the inquiry is the same: the study of the growth of a crystal 
differing from that of a plant or an animal not in kind but 
only in degree; the investigation being in each case the re- 
distribution of matter, for there is nothing in the crystal that 
did not pre-exist in the saline solution, nothing in the plant 
that was not derived from the seed or the soil, nothing in 
the chicken that did not pre-exist in the egg or in the air. 
The ultimate cause of the so-called Vital Force is as un- 
knowable as the cause of all other kinds of Force. The 
laws, however, by which the effects of the so-called Vital 
