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 water 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- 
