Page:Popular Science Monthly Volume 9.djvu/111

Rh whose ideas he upheld. Soon after began the great controversy between Needham and Spallanzani, who refuted, by experiment, the conclusions arrived at by Needham.

The controversy turned principally on this point: Spallanzani was not satisfied with heating the hermetically-sealed vessels containing the infusions, for several minutes, merely the time which is required to cook a hen's-egg, and to destroy the germs, as Needham expresses it, but he kept them for the space of an hour in boiling water. He then observed no production of infusoria. But, objects the English observer, from the manner in which he treated and put to the torture his nineteen vegetable infusions, it is evident that he not only much weakened, or perhaps totally destroyed, the vegetative force of the substances infused, but also entirely corrupted, by the exhalations and the odor of the fire, the small portion of air which remained in the empty part of his vessels. It is not, therefore, surprising that his infusions, thus treated, gave no signs of life. Such must necessarily have been the case. This idea, that the action of the temperature of boiling water destroys the vegetative force of infusions, is maintained even at the present day, and has served as an argument to the heterogenists; as they were unable to attack the material correctness of Pasteur's experiments, they did not accept the conclusions which he sought to derive from them.

We find also in the passage just cited, the necessity for the experiments made by Schwann and Helmholtz on calcined air, and for those of Schröder and F. Dusch, on strained air. The objection of a possible change in the air contained in the vial, under the influence of prolonged boiling, in presence of organic substances, was a serious one at the time that it was brought forward; it becomes more so, when we know that the air confined over preserved meats, prepared by Appert's process, contains no oxygen. It was, therefore, absolutely necessary to place the infusions in contact with air in a normal condition, after that boiling had deprived them of their preëxisting germs, avoiding at the same time any new germs brought by the air.

For this purpose, Dr. Schwann heated flasks containing the infusions, until the destruction of the germs was insured; but his flask was not closed: it communicated freely with the surrounding air by mean of a glass tube bent in the form of a U, and heated, in one part of its length, by means of a bath of fusible alloy. Under these conditions, the air may be renewed in the flasks, but the fresh atmospheric air admitted has undergone, like the infusion, the action of heat, which destroys the germs. Schwann's experiment was very decisive, as to broth made from meat; and the negative result (no development of infusoria) was quite satisfactory. But it was not the same with analogous trials on alcoholic fermentation, which gave contradictory results. Ure and Helmholtz repeated and multiplied these experiments with the same success.