ch. viii.] THE BEGINNINGS OF LIFE. 421 



" theory of omnipresent germs," or (less cumbrously) as the 

 " germ-theory." 



Now, as concerns the germ-theory, to which appeal is un- 

 hesitatiugly made whenever the question of spontaneous 

 generation is discussed, it must be admitted to be extremely 

 plausible, yet we must not forget that it has never been 

 actually demonstrated : it has not been proved that the 

 germ-theory can do all that its advocates require it to do. 

 It may well be the case that the air is everywhere full of 

 germs, too small to be seen, which are capable of giving 

 rise to all the organisms of which there is any question in 

 the controversy about spontaneous generation : nevertheless 

 this has not been rigorously demonstrated. The beautiful 

 researches of Prof. Tyndall have indeed proved that the atmo- 

 sphere is everywhere filled with solid particles, in the absence 

 of which it would not be luminous ; and it is fair to suppose 

 that among these particles there are always to be found some 

 which are the germs of monads and bacteria. Still this can 

 hardly be taken for granted ; and Dr. Bastian is right in 

 reminding us that it is reasoning in a circle to assume the 

 presence of germs that cannot be detected, merely because 

 there is no other way of accounting for the presence of 

 monads and bacteria in accordance with the doctrine of Eedi. 



For in all discussions concerning spontaneous generation 

 it should be borne in mind that the doctrine omne vivum ex 

 vivo is itself on trial for its life, and cannot be summoned 

 to the witness-box. The very point to be ascertained is 

 whether this doctrine, which is admitted to hold good in 

 the case of all save the lowest forms of life, holds good also 

 of these. The doctrine rests entirely upon induction ; and 

 while, in many cases, it is legitimate to infer a universal 

 proposition from a limited induction of instances, it is not 

 legitimate to do so in the present case. For the fact that 

 innumerable highly specialized types of animal and vegetal 

 life are kept up solely by generation ex vivo, can in nowise 



