Fig. 4.—Schwann’s experiment. After boiling, as shown in the diagram, and cooling, air was drawn into the flask by aspiration while the coiled tube was kept hot with the flame.
Fig. 5.—Schroeder and Dusch’s experiment. The aspirating bottle drew the air through the flask after it had been filtered by the cotton in the tube.
Fig. 6.—Pasteur’s flask.
Fig. 7.—Tyndall’s box. One side is removed to show the construction. The bent tubes at the top are to permit a free circulation of air into the interior. The window at the back has one corresponding in the front (removed). Through these the beam of light sent through from the lamp at the side was observed. The three tubes received the infusion and were then boiled in an oil bath. The pipette was for filling the tubes. (Popular Science Monthly, April, 1877.).
John Tyndall, in combating Bastian’s views showed that boiled infusions left open to the air in a closed box through which air circulated did not show any growth of organisms provided the air was so free of particles that the path of a ray of light sent through it from side to side could not be seen ([Fig. 7]). Or if such sterilized infusions were exposed to dust-free air, as in the high Alps, the majority showed no growth, while all infusions in dusty air did show an abundance of organisms. Tyndall’s experiments confirmed those of Pasteur and his predecessors and showed that the organisms developed from “germs” present in the air falling into the liquids and not spontaneously.
While Tyndall’s experiments were of great value as indicated, they probably were harmful in another way. These “germs in the air” were considered by bacteriologists as well as laymen to include necessarily many disease germs and to indicate the very general, if not universal, presence of these latter in the air. This idea led to many erroneous practices in sanitation and disinfection which even to this day are not eliminated.