THE QUESTION OF SPONTANEOUS GENERATION. 97 



beam of light. There then appeared, dancing and twirl- 

 ing in the beam, thousands of little particles of dust. 



'If we had time to examine them well,' continued 

 Pasteur, 'we should see them, though agitated with 

 various movements, falling downwards more or less 

 quickly. It is thus that all objects become covered 

 with dust the furniture, the table, the mercury in 

 this basin. Since this mercury was taken from the 

 mine, how much dust must have fallen upon it, to say 

 nothing of all that has been intimately mixed up 

 with it during the numerous manipulations to which 

 it has been subjected in the laboratory ? It is not 

 possible to touch this mercury, to place the hand in 

 it, or a bottle, without introducing into the interior of 

 the basin the dust which lies on its surface. You 

 will now see what takes place.' 



Projecting, in the darkness, the beam of light upon 

 the basin of mercury, the liquid metal shone forth with 

 its usual brilliancy. Pasteur then sprinkled some dust 

 upon the mercury, and, plunging a glass rod into it, 

 the dust was seen to travel towards the spot where 

 the rod entered the mercury, and to penetrate into the 

 space between the glass and the metal. 



' Yes,' exclaimed Pasteur with a voice which gave 

 evidence of the sincerity of his conviction, 'yes, M. 

 Pouchet had removed the germs from the water and 

 from the hay, but he had neglected to remove the 

 dust from the surface of the mercury. This is the 



