x.] BIOGENESIS AND ABIOGENESIS. 231 



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 proportion of its oxygen, while it 

 must needs arrest, or destroy, any organic matter which 

 may be contained in the air. These experimenters, there- 

 fore, contrived arrangements 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 aoid. 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 

 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 ; that it consisted of germs remained only 

 an hypothesis of greater or less probability. 



Contemporaneously with these investigations a remark- 

 able discovery was made by Cagniard de la Tour. He 

 found that common yeast is composed of a vast accumu- 

 lation of minute plants. The fermentation of must, or of 

 wort, in the fabrication of wine and of beer, is always 

 accompanied by the rapid growth and multiplication 

 of these Torulce. Thus, fermentation, in so far as it 

 was accompanied by the development of microscopical 

 organisms in enormous numbers, became assimilated to 

 the decomposition of an infusion of ordinary animal or 

 vegetable matter ; and it was an obvious suggestion that 

 the organisms were, in some way or other, the causes 



