To obviate the objection of a possible change by heat, in a mysterious and undefined principle, different from germs, but whose presence in the air was necessary to the production of infusoria, Schultze caused the renewed air to pass through energetic chemical reagents, such as concentrated sulphuric acid. He half filled a glass vessel with distilled water containing various animal and vegetable substances; then stopped the vessel with a cork through which passed two bent tubes, and exposed the apparatus thus arranged to the temperature of boiling water. Then, while the vapor was still escaping through the tubes, he adapted to each of them a Liebig's bulb apparatus, one containing concentrated sulphuric acid, and the other concentrated caustic potash. The high temperature must necessarily have destroyed every living thing, all the germs that might happen to be in the inside of the vessel, or of its appendages, and the communication from without was intercepted by the sulphuric acid on one side and the potassa on the other. Nevertheless, it was easy to renew, by aspiration at the end of the apparatus which contained the potassa, the air thus inclosed, and the fresh quantities of this fluid which were introduced could not carry with them any living germ, for they were forced to pass through a bath of concentrated sulphuric acid. M. Schultze placed the apparatus thus arranged at a well-lighted window, side by side with an open vessel, which contained an infusion of the same organic substances; then he was careful to renew the air in his apparatus several times a day for more than two months, and to examine with the microscope what took place in the infusion. The open vessel was soon found filled with vibrios and monads, to which were soon added polygastric infusoria of a larger size, and even rotifers; but by the most attentive observation he could not discover the least trace of infusoria, confervæ, or mildews, in the infusion contained in the apparatus.
The latest researches of Schröder and Von Dusch (1854-1859) tended to raise another objection, the possible change in a special principle in the air, by a reagent as energetic as sulphuric acid. Guided by the experiments of Loëwel, who ascertained that common air, when it had been previously filtered through cotton, was unfit to cause the crystallization of supersaturated solutions of sodium sulphate, they placed one of the tubes of Schultze's apparatus in communication with a tube 1.18 inch in diameter, and from 19.68 to 23.62 inches in length, tilled with cotton-wool. The other tube was connected with an aspirator.
When the liquid, the interior of the flask, and the tubes, had been deprived of air by boiling, the apparatus was removed to its place, and the aspiration continued night and day. The two observers thus proved that meat, to which water had been added, the wort of beer, urine, starch, paste, and the various materials of milk taken separately, remained intact in the filtered air. On the contrary, milk, meat
