VIII BIOGENESIS AND ABIOGENESIS 245 



three-quarters of an hour, 1 no animalcules ever 

 made their appearance within them. It must be 

 admitted that the experiments and arguments of 

 Spallanzani furnish a complete and a crushing 

 reply to those of Needham. But we all too often 

 forget that it is one thing to refute a proposition, 

 and another to prove the truth of a doctrine which, 

 implicitly or explicitly, contradicts that propo- 

 sition ; and the advance of science soon showed 

 that though Needham might be quite wrong, it 

 did not follow that Spallanzani was quite right. 



Modern Chemistry, the birth of the latter half 

 of the eighteenth century, grew apace, and soon 

 found herself face to face with the great problems 

 which biology had vainly tried to attack without 

 her help. The discovery of oxygen led to the lay- 

 ing of the foundations of a scientific theory of 

 respiration, and to an examination of the marvel- 

 lous interactions of organic substances with 

 oxygen. The presence of free oxygen appeared to 

 be one of the conditions of the existence of life, 

 and of those singular changes in organic matters 

 which are known as fermentation and putrefaction. 

 The question of the generation of the infusory 

 animalcules thus passed into a new phase. For 

 what might not have happened to the organic 

 matter of the infusions, or to the oxygen of the 

 air, in Spallanzani's experiments ? What security 

 was there that the development of life which ought 

 1 See Spallanzani, Opere, vi. pp. 42 and 51. 



