26 BIOLOGY: GENERAL AND MEDICAL 



protected by a plug of cotton-wool through which an 

 abundance of air could freely enter and exit, but by 

 which it would be filtered, no life appeared in the contents. 

 The investigation was continued in 1861 by Pasteur, 

 who showed that if the neck of a flask containing putres- 

 cible fluid was drawn out into a fine tube, bent down along 

 the side of the flask, and then bent up again so as to form 

 a V, it could be left open, after the contents of the flask 

 had been thoroughly boiled, without danger of contami- 

 nation from the outside air, which, entering through the 



FIG. 1. Flask used by Pasteur in his experiments upon the spontaneous 

 generation of life. It was filled through the top which was then sealed. The 

 contents, which consisted of putrescible fluid were then boiled, the side neck 

 being open to permit the air to enter and exit. As the fluid cooled the side 

 neck became closed by a few drops of water of condensation and prevented any 

 germs of life from entering from without. 



tubulature, would have any germs it might contain 

 arrested by the drop of water of condensation that always 

 collected in the angle of the tube. 



Tyndall performed a most interesting series of experi- 

 ments in which tubes were so placed as to project below 

 the bottom of a closed chamber having a glass front and 

 a glass window in each side. A rubber diaphragm was 

 fixed in the roof through which a tube passed. Tyndall 

 found that a ray of light passed through the side windows 

 of the chamber was visible from the front because it was 

 reflected from the dust particles suspended in the atmos- 



