The Conditions of Life and Death. 97 



After Spallanzani's experiments the discussion took 

 another turn. It was objected by the chemists, who 

 had now discovered oxygen, that life could not be ex- 

 pected where this gas was more or less absent, and 

 that the boiling process might irretrievably injure the 

 "organic molecules". Schultze and Schwann (1836, 

 1837) were thus led to make fresh experiments; they 

 carefully boiled the infusions and supplied air which 

 had been passed through red-hot tubes, no animal- 

 cules appeared; they then supplied air which had not 

 been so purified, and in the same infusions the animal- 

 cules appeared. This was improved upon by Schroeder 

 and Dusch (1854-59), who did what we now so often 

 do as a class experiment: they boiled infusions, and 

 while the steam was coming off plugged the neck of the 

 flask with cotton-wool. This allows the passage of 

 oxygen, but keeps back germs ; and in most cases the 

 sterilization is quite effective. Meanwhile Schwann and 

 Cagniard de la Tour had been working towards the 

 conclusion for which Pasteur did so much to win con- 

 viction, that all putrefaction and many kinds of fermen- 

 tation are due to the activity of minute living organisms. 

 Thus the discussion narrowed till there was, it might 

 have seemed, no debatable point left. 



But error dies hard, and in 1859 Pouchet published 

 his Hdtrognie y in which almost all that could be said 

 in favour of spontaneous generation was Pouchet and 

 again said. In 1858 he had claimed before Pasteur, 

 the Academy of Sciences that he had succeeded in 

 proving the origin of microscopic organisms apart from 

 pre-existing germs. The historical interest of Pouchet' s 

 work in this connection is simply that it provoked Pas- 

 teur, against the advice of his friends, to some of his 

 fine work. Pasteur knew more than Pouchet as to the 

 insidious ways of microbes ; he showed the weak point 

 of his antagonist's experiments, and gained the prize 

 offered in 1860 by the Academy, for " well-contrived 

 experiments to throw new light upon the question of 

 spontaneous generation ". Pasteur threw light on the 

 subject by his study of the organized particles many 

 of them living or dead bacteria which float in the air, 



(X628) 3 



