358 LAY SERMONS, ADDRESSES, AND REVIEWS. [xv. 



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 composition of the organic matter, was altered 

 in such a matter as to interfere with the existence of 

 life. 



Schulze and Schwann took up the question from 

 this point of view in 1836 and 1837. The passage of 

 air through red-hot glass tubes, or through strong 

 sulphuric acid, does not alter the proportion of its 

 oxygen, while it must needs arrest or destroy any 

 organic matter which may be contained in the air. 

 These experimenters, therefore, contrived arrange- 

 ments by which the only air which should come into 

 contact with a boiled infusion should be such as had 

 either passed through red-hot tubes or through strong 

 sulphuric acid. The result which they obtained was 

 that an infusion so treated developed no living things, 

 while, if the same infusion was afterwards exposed to 

 the air, such things appeared rapidly and abundantly. 

 The accuracy of these experiments has been alternate- 

 ly denied and affirmed. Supposing them to be ac- 

 cepted, however, all that they really proved was that 

 the treatment to which the air was subjected destroyed 

 something that was essential to the development of life 

 in the infusion. This " something " might be gaseous. 



