Philosophical Conceptions of Life. 249 
existence of which I believe as firmly as I believe in the 
existence of force, although I do not know its nature any 
more than I know the nature of force. If, for convenience, 
at any time [ compare the living body to a machine, I must 
compare the vital principle to the engineer ; it is the director, 
the manager if you will, but it does not supply the force that 
does any part of the work. Let us consider, then, in the 
remainder of this discourse the phenomena which indicate the 
guidance of the vital principle. 
The first group of phenomena belonging to this second 
class are those forced upon our attention whenever we attempt 
to study the question of the origin of life. It has seemed to 
some of our contemporaries that, in accordance with the doc- 
trine of evolution, as deduced by Mr. Herbert Spencer from 
the great truth of the persistence of force, life ought always 
to arise spontaneously out of inorganic matter whenever the 
necessary materials and other conditions of life are brought 
together. Indeed, if there be nothing more or other in life 
than force, I confess I do not understand how this conclusion 
can be logically escaped; and yet when we come to interrogate 
nature we find that, in point of fact, things do not happen so. 
The sun may stream all the enormous energy of his rays 
upon the slime of the Nile, but he generates no monsters ; 
nay, not even a bacterium, except in the presence and under 
the direction of pre-existing life. Our biological knowledge has 
so far advanced that it is easy for us to get together mixtures 
of matter, for the most part derived from pre-existing living 
beings, which are peculiarly well fitted to supply the materials 
needed for the building up of a variety of low forms of 
life ; and the extent of our present knowledge of the conditions 
favourable to the development of these low forms of life is 
shown by the rapidity with which they do develop from a 
few individuals to countless millions, if only a few indivi- 
duals are introduced as parents into our flasks and brood- 
ovens. ‘The species to which the countless progeny belongs, 
depends always upon the species of the parents we introduced 
by design or accident ; and if parents of several species are 
introduced we may imitate on a tiny scale the great struggle 
for existence, and witness the survival of the fittest. Never, 
however, has the spontaneous generation, out of inorganic 
matter, of a single living form been yet observed. — 
Speculative considerations have, indeed, from time to time 
led certain enthusiasts to desire earnestly that it might be 
observed; and when we consider, on the one hand, the influ- 
ence of pre-existing bias, and, on the other, the intricacy of 
some of the experimental processes in question, it is by no 
Ann. & Mag. N. Hist. Ser. 5. Vol. xiii. 17 
