42 THE MICROSCOPE. Mar. 



ing matter around it and the hot air from the flame arose 

 into the beam and pushed aside the illuminated particles 

 and substituted its own perfect transparency. 



Tyndall brought this discovery to bear upon the study 

 of spontaneous generation. He reasoned that if an infu- 

 sion, barren, but susceptible of putrefaction when exposed 

 to ordinary air was brought into contact with this non- 

 luminous air it would never putrefy. To prevent the 

 objection ; that oxygen passed through a spirit lamp 

 flame looses its vitalizing properties he performed the 

 following experiment : a condensed beam was sent 

 through a large flask containing air ; the light revealed 

 the dust in the jar. The jar was corked and left for a few 

 days and examined with the luminous beam ; no track 

 was visible, the floating matter had settled on the sides 

 of the vessel. Here he found a way of ridding the air 

 of its floating matter without burning it. He then con- 

 structed wooden chambers (c) having glass fronts, side 

 windows and back doors. Through the bottom of the 

 chamber test tubes {dd) were passed air tight, their open 

 ends within the chamber (c). He connected the inner 

 and outer air by means of sinuous channels (/. g.) through 

 which air could pass but no dust. A pipette (e) entered 

 the chamber from the top. Every precaution was taken 

 to prevent dust from passing into the chamber. The 

 chamber was then closed and permitted to remain quiet 

 for two or three days. Examined at the beginning by a 

 beam sent through its windows (a. h.) the air was found 

 laden with floating matter which in three* dayshad wholly 

 disappeared. The inside was coated with glycerine to 

 prevent it rising again. The fresh liquid was introduced 

 into the tubes by means of the pipette. The tubes were 

 then put into a bath and contents boiled to destroy the 

 infection which it had received from air before it was 

 put in the tubes. 



With such chambers, Tyndall tested infusions of the 



