ch. viii.] THE BEGINNINGS OF LIFE. 427 



statement of it. As practically conducted, the dispute is 

 confined to the question whether certain particular low forms 

 of life — known as vibrios, bacteria, torulse, and monads — 

 which appear in putrescence or in fermentation, are produced 

 by archebiosis, or are propagated from germs conveyed in the 

 atmosphere. 



If Dr. Bastian's position with reference to this question is 

 destined to become substantiated, his work may perhaps 

 mark an epoch in biology hardly less important than that 

 which was inaugurated by Mr. Darwin's " Origin of Species." 

 Unfortunately, the kind of proof which is needed for Dr. 

 Bastian's main thesis is much more difficult, both to obtain, 

 and to estimate properly, than the kind of proof by which 

 the theory of natural selection has been substantiated. In 

 the latter case what was needed was some principle of 

 interpretation which should account for the facts of the 

 classification, embryology, morphology, and distribution of 

 plants and animals, without appealing to any other agencies 

 than such as can be proved to be actually in operation ; and 

 it is because the theory of natural selection furnishes such 

 a principle of interpretation that it has met with such ready 

 acceptance from the scientific world. 1 On the other hand, 

 the fate of the theory of archebiosis, in the shape in which 

 it is held by Dr. Bastian, depends upon the issue of a series 

 of experiments of extraordinary delicacy and difficulty, — 

 experiments which are of value only when performed by 

 scientific experts of consummate training, and which the 

 soundest critic of inductive methods must find it perilous to 

 interpret with confidence, unless he has had something of 

 the training of an expert himself. For however easy it may 

 seem to the uninitiated to shut up an organizable solution so 

 securely that organic germs from the atmosphere cannot even 

 be imagined capable of gaining access to it, this is really one 

 »f the most arduous tasks which an experimenter has ever 

 1 1 am here anticipating the argument of the two following chapters. 



