246 BIOGENESIS AND AB1OGENESIS vili 



to have taken place had not been checked or pre- 

 vented by these changes ? 



The battle had to be fought again. It was need- 

 ful 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 manner 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 propor- 

 tion of its oxygen, while it must needs arrest, or 

 destroy, any organic matter which may be con- 

 tained in the air. These experimenters, therefore, 

 contrived arrangements by which the only air 

 which should come into contact with a boiled in- 

 fusion should be such as had either passed through 

 red-hot tubes or through strong sulphuric acid. 

 The result which they obtained was that an in- 

 fusion 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 

 alternately denied and affirmed. Supposing them 

 to be accepted, 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, fluid, or solid; 



