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that they can detach portions of their own substance which 
may be developed into new individuals. How, then, do we 
explain the fact that living bodies exhibit these phenomena, 
so different in their essence to anything observable in dead 
matter? In other words, what is the nature of “life,” 
and what is its connection with the matter by which it is 
manifested ? 
In dealing with this question,* we have two classes of 
theories to consider — namely, the physical or material , and the 
so-called vitalistic. It is not meant by this that there are only 
two theories commonly held as to the nature of life, but 
simply that all existing theories, however diverse, may be - 
reduced to one or other of these categories. First, as to 
the physical theories. The ordinary physical phenomena of 
matter appear beyond question to be due simply to movements 
taking place in the ultimate molecules of which matter is 
composed. These movements may vary in amount and in 
kind, and may thus give rise to the most diverse phenomena, 
but they are all essentially of the same nature. Hence, so 
far as dead matter is concerned, there is no impropriety in 
saying that force is simply an affection of matter. You might 
have the matter without the force ; but you cannot have the 
force, or its resultant phenomena, without the matter. 
The advocates of the physical doctrine of life stretch this 
admission beyond the limits here assigned to it, and embrace 
in its scope all the phenomena of vitality. On this theory all 
vital actions are reduced to molecular movements of the proto- 
plasm of which the living body is composed. The properties 
of living beings are asserted to be “as much dependent upon 
the mere qualities and nature of the material aggregate which 
displays them, as the properties of a metal, or the properties 
of a crystal, are the results of the nature and mode of colloca- 
tion of the atoms of which these bodies are composed.” — 
(Bastian.) On this view, therefore, “Life” is merely a form 
of energy or motion , and the vital forces of the organism are 
merely correlates of the ordinary physical forces. To put it 
in another form, the mechanical, chemical, and physical phe- 
nomena of the organism are wholly the result of transforma- 
tions of the heed which it receives from the sun, and the 
energy stored up in its food. 
As opposed to the doctrines of the physical school, we have 
the views held by the so-called “ vitalists.” In its crudest 
* The following remarks as to the physical and vitalistic theories of life 
are taken from the inaugural lecture to the class of Natural History in the 
University of St. Andrews, delivered in 1875. 
