104 LOUIS PASTEUR 



vacation ground in the Alps with results corrobo- 

 rating those obtained by Pasteur. Many experi- 

 ments were carried on with an apparatus constructed 

 as follows: A case with glass front and a glass 

 window in either side (Fig. 10) is provided with a 

 bottom having holes in which glass test tubes are 

 fixed, air tight, with their open upper ends in the 

 chamber. Through the top is a funnel tube passing 

 through an India rubber disc. This tube is movable 

 and is used for filling the tubes with liquid. Two 

 tubes are fitted for admitting air, but they are bent 

 several times to intercept any floating matter that 

 might be carried by the slow exchange of air be- 

 tween the inside and the outside of the chamber. 

 The inside of the chamber is coated with glycerine 

 to catch any floating motes which come in contact 

 with it. 



A powerful beam of light sent through the glass 

 windows revealed the existence of floating particles 

 in its course. After a time the beam became less 

 and less visible as the motes in the air settled to 

 the bottom or were caught by the coating of glyc- 

 erine on the top and sides. In three days the beam 

 within the box was quite invisible, but before it 

 entered the box and after it emerged its track was 

 "vivid in the air." 



