PHILOSOPHICAL SOCIETY OF WASHINGTON. 65 



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 con- 

 clusion can be logically escaped ; and yet, when we come to inter- 

 rogate 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 knowl- 

 edge of the conditions favorable 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 individ- 

 uals 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 sur- 

 vival of the fittest. Never, however, has the spontaneous genera- 

 tion, out of inorganic matter, of a single living form been yet ob- 

 served. 



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 influence of pre-existing 

 bias, and on the other the intricacy of some of the experimental 

 processes in question, it is by no means necessary to charge dishon- 

 esty upon those who, from time to time, have actually fancied that 

 their desires have been realized to the extent of the spontaneous 

 generation of bacteria at least. When we consider the immense 

 development of the trade in canned food, which could not exist for 

 a single summer's day, if these experimenters were not mistaken, it 

 will be seen how little need there was for renewed scientific experi- 

 ment to refute their conclusions ; but it is a noteworthy fact that 

 among those who have contributed most by exact research to recent 

 scientific demonstrations of the truth, that life never arises except 

 from pre-existing life, are to be found some of the most earnest and 

 eloquent advocates not merely of the doctrines of evolution, but of 

 its supposed corollary, the chemico-physical hypothesis of life. 

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