244 



HOW LIFE BEGAN 



in more germs and the organic material would then decompose and 

 show numerous microorganisms. If care were taken that no 

 air entered, no organisms appeared. He repeated Pouchet's first 

 experiment and showed a source of probable error. In a darkened 

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

 audience saw that the surface of the mercury was covered with 

 dust particles. Pasteur showed that when the forceps were 

 plunged through the mercury, they took some of the dust particles 

 with them. He then explained that the floating particles of dust 

 contained living germs. Later, the Commission decided that the 

 contest should be settled by one experiment. Pouchet wanted 

 more. The Commission refused and gave its decision in favor of 

 Pasteur. 



John Tyndall. In 1876, John Tyndall, an English physicist, 

 published the results of his experiments. He had devised a very 

 elaborate box or chamber which enclosed a volume of air. This 



was so regulated that any 

 particles floating in the air 

 would settle and be held on 

 a sticky substance, such as 

 glycerine, spread over the 

 sides of the box. Tyndall 

 passed a powerful beam of 

 light through an opening 

 in the box to make sure 

 that no free dust particles 

 were present in the air. If 

 dust particles were present 

 in the air, the beam of 

 light would illuminate 

 them. Then he applied heat to the test tubes of nutritive fluids 

 that were suspended in the box. These fluids consisted of mutton 

 broth, turnip broth, and fluids from other plants and animals. 



Tyndall's apparatus added further data which 

 helped disprove the theory of spontaneous genera- 

 tion. Identify the different parts of the apparatus 

 from the description given in the text. 



