20 PATHOGENIC BACTERIA. 



who repeated his experiment, under the conditions that 

 he regarded as certainly excluding all life, germs can 

 readily enter with the air. 



The term "infusorial life" having been used, here it 

 is well to observe that during all the early part of their 

 recognized existence the bacteria were regarded as ani- 

 mal organisms and classed among the infusoria. 



Tyndall, stimulated by the work of Pasteur, con- 

 clusively proved that the micro-organismal germs were 

 in the dust suspended in the atmosphere, not ubiquitous 

 in their distribution. His experiments were very ingen- 

 ious and are of much interest. First preparing light 

 wooden chambers, with one large glass window in the 

 front and one smaller window in each side, he arranged a 

 series of test-tubes in the bottom, half in and half out of 

 the chamber, and a pipette in the top, working through 

 a rubber diaphragm, so that when desired the tubes, one 

 by one, could be filled through it. The chamber was 

 first allowed to stand until all the contained dust had 

 settled, and was then submitted to an optical test to de- 

 termine the purity of its atmosphere, a powerful ray of 

 light being passed through the side windows. When 

 viewed through the front window, this ray was visible 

 as long as there were particles suspended in the atmo- 

 sphere to reflect it. When the dust had completely 

 settled and the light ray was invisible because of the 

 purity of the atmosphere, the tubes were cautiously 

 filled with urine, beef-broth, and a variety of animal and 

 vegetable broths, great care being taken that in the 

 manipulation the pipette should not disturb the dust. 

 Their contents were then boiled by submergence in a 

 pan of hot brine placed beneath the chamber, in con- 

 tact with the projecting ends of the tubes, and allowed 

 to remain undisturbed for days, weeks, or months. In 

 nearly every case life failed to develop after the purity of 

 the atmosphere was established. 



The following extracts from Tyndall' s work 1 will illus- 



1 Op. cit. 



