286 BIOLOGY AND ITS MAKERS 
that the bent tube on one side was surrounded by a jacket 
of metal and was subjected to a very high temperature while 
the air was being drawn through it, the effect being to kill 
any floating germs that might exist in the air. Great care 
was taken by both experimenters to have their flasks and fluids 
thoroughly sterilized, and the results of their experiments were 
to show that the nutrient fluids remained uncontaminated. 
These experiments proved that there is something in 
the atmosphere which, unless it be removed or rendered 
inactive, produces life within nutrient fluids, but whether 
this something is solid, fluid, or gaseous did not appear 
from the experiments. It remained for Helmholtz to show, 
as he did in 1843, that this something will not pass through 
a moist animal membrane, and is therefore a solid. The 
results so far reached satisfied the minds of scientific men, 
and the question of the spontaneous origin of life was 
regarded as having been finally set at rest. 
III. The Third Period. Pouchet——We come now to con- 
sider the third historical phase of this question. Although it 
had apparently been set at rest, the question was unexpect- 
edly opened again in 1859 by the Frenchman Pouchet, the 
director of the Natural History Museum of Rouen. The 
frame of mind which Pouchet brought to his experimental 
investigations was fatal to unbiased conclusions: ‘When, 
by meditation,” he says, in the opening paragraph of his book 
on Heterogenesis, “it was evident to me that spontaneous 
generation was one of thc means employed by nature for the 
production of living beings, I applied myself to discover by 
what means one could place these phenomena in evidence.” 
Although he experimented, his case was prejudiced by 
metaphysical considerations. He repeated the experiments 
of previous observers with opposite results, and therefore he 
declared his belief in the falsity of the conclusions of Spal- 
lanzani, Schulze, and Schwann. 
