The true scientific difficulty, however, was determination of a reliable test for destruction of germinal forms, either adhering to the materials, embedded in them, or floating in the atmosphere. The history of observations bearing on this question is deeply interesting. In the earlier tentative experiments, the material placed under observation was boiled; it was concluded that no vital organism could endure this process; and the material was kept for a time in a temperature of from seventy to eighty degrees Fahr., which was regarded as favorable to the development of life. In process of time, a deposit appeared in the tube, and this when examined under the microscope was found to contain bacteria,[H] living, moving germinal forms so minute as to require high magnifying power for their discovery. Here then was "spontaneous generation." Who could be so credulous as to believe that minute organic forms could live through the boiling process? If this appeared too absurd to fancy, then spontaneous generation, or actual origin of life out of non-organized matter, must be held to be established. It was only the audacity of prejudice, and hopeless alienation from the "advanced thought" of the time, which could induce any one to doubt, in face of these experiments, carefully recorded and published.[I] Scientific observers of great experience and reputation felt it needful to express themselves with caution, leaving results to be tested. A considerable number of investigators began to turn their attention to the subject, and a period of seven years was occupied before the results became so certain as to be practically final. Pasteur, Pouchet, and Joubert were at work in France, Crookes, Child, Beale, Roberts, Bastian, Tyndall and others in England.