230 CRITIQUES AND ADDRESSES. [x. 



infusions were contained were hermetically sealed by fusing 

 their necks, and if, in the second place, they were ex- 

 posed to the temperature of boiling water for three-quarters 

 of an hour, 1 no animalcules ever made their appear- 

 ance within them. It must be admitted that the experi- 

 ments 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 proposition; 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 laying of the foundations of a sci- 

 entific theory of respiration, and to an examination of 

 the marvellous 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 to have 

 taken place had not been checked or prevented by these 

 changes ? 



The battle had to be fought again. It was needful to 

 repeat the experiments under conditions which would 

 make sure that neither the oxygen of the air, nor the 



1 See Spallanzaui, " Opere," vi. pp. 42 and 51. 



