When dealing with bacteria, he found that they differed from other forms in this, that they rose to the air as if it were a requisite, whereas other germs, such as those belonging to the process of fermentation, could exist without oxygen. This led to an additional form of experiment, with the view of deciding whether bacteria could be destroyed by withdrawal of air; and if so, whether the bacteria would reappear after the existing microscopic life had been stifled. Tyndall began by applying the air-pump. Under this process the bacteria were enfeebled greatly, but not destroyed. Thereafter Sprengel pumps were used, by means of which the air dissolved in the infusions was withdrawn, as well as that diffused in the spaces above. In numerous cases there was success in destroying the germs by removal of the air in this way without any boiling process. In these cases, the air was carefully restored, precautions being adopted to guard against admission of germinal forms, and in no case did life reappear in the infusions. As in the more common style of experiment, the warmth suitable could not charm the life back again; so in this, the restoration of oxygen, could not secure restoration of life. Thus evidence from all sides directed surely to the conclusion that the alleged discovery of "spontaneous generation" was a delusion, the result of hasty and insufficient experiment. Dr. Bastian, nevertheless, stuck heroically to his original position, and came into conflict with M. Pasteur of Paris, by means of a communication which the English Professor had sent to the Academy of Sciences in July of the previous year, 1876. In the beginning of 1877, M. Pasteur threw down an explicit challenge to Professor Bastian, which resulted in the appointment of a commission to observe the experiments and adjudicate. With this terminates the history of nearly ten years of curious and singular investigation, and Dr. Bastian himself has supplied the history of the closing scene, laying open the whole correspondence to public investigation, as if he were unconscious of the complete demolition of his favorite theory of "spontaneous generation." The 15th of July, 1877, witnessed the close of a battle he had been fighting against steadily increasing odds, and which he had begun in June, 1870. Dr. Bastian's position was "that a solution of boiled potash caused bacteria to appear in sterile urine at fifty degrees Cent., added in a quantity sufficient to neutralize the latter." These he regarded as the physico-chemical conditions for spontaneous generation of bacteria.