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 uncontaminatcd. 



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 tn ^ s 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 Heter -agenesis, "it was evident to me that spontaneous 

 generation was one of the means employed by nature for the 

 production of living beings, I applied myself to discover by 

 w T hat 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. 



