288 BIOLOGY AND ITS MAKERS 



duced into the water." He declared that this life was, there- 

 fore, of spontaneous origin. 



The controversy now revived, and waxed warm under the 

 insistence of Pouchet and his adherents. Finally the Acad- 

 emy of Sciences, in the hope of bringing it to a conclusion, 

 appointed a committee to decide upon conflicting claims. 



Pasteur. Pasteur had entered into the investigation of 

 the subject about 1860, and, with wonderful skill and acumen, 

 was removing all possible grounds for the conclusions of 

 Pouchet and his followers. In 1864, before a brilliant 

 audience at the Sorbonne, he repeated the experiment out- 

 lined above and showed the source of error. In a darkened 

 room he directed a bright beam of light upon the apparatus, 

 and his auditors could see in the intense illumination that 

 the surface of the mercury was covered with dust particles. 

 Pasteur then showed that when a body was plunged beneath 

 the mercury, some of these surface granules were carried 

 with it. In this striking manner Pasteur demonstrated 

 that particles from the outside had been introduced into the 

 bottle of w r ater by Pouchet. This, however, is probably not 

 the only source of the organisms which were developed in 

 Pouchet's infusions. It is now known that a hay infusion 

 is very difficult to sterilize by heat, and it is altogether likely 

 that the infusions used by Pouchet were not completely 

 sterilized. 



The investigation of the question requires more critical 

 methods than was at first supposed, and more factors enter 

 into its solution than were realized by Spallanzani and 

 Schwann. 



Pasteur demonstrated that the floating particles of the air 

 contained living germs, by catching them in the meshes of 

 gun cotton, and then dissolving the cotton with ether and 

 examining the residue. He also showed that sterilized 

 organic fluids could be protected by a plug of cotton suffi- 



