days. Did the genetic power then wait for the disappear- ance of this swan's neck in order to manifest itself? What is your explanation worth in the presence of this: the curves of the neck, remaining moist at the moment when the fire was extinguished, washed in its passage the air which traversed them in a thin thread? In the beginning when the entrance of the air was rapid, the purifying action of this washing was doubled by that of FIG. 12. --Swan-neck flank used by Pasteur in his study of spontaneous generation. the liquid, still hot and able to destroy the germs which came in contact with it. Later, the wet. walls of the neck have held fast the germs of the air as they have passed through the narrow opening. The proof of this is that if you shake the flask in such a way as to introduce into the curve of the neck a little drop of the infusion, having previously closed the open end so that nothing new will enter, this drop becomes clouded, and if you then mix this drop with the rest of the liquid, the latter -99- |