The selection of materials to experiment upon was for a time according to the fancy of the experimenter. It was not proposed that a vacuum should be made by withdrawal of all air from a glass vessel, thereafter watching for the appearance of some organic form. Nor was it suggested that pure water might be taken from a spring, and boiled, and left standing under daily observation. A great variety of materials was selected to provide an infusion which might afford the conditions for application of scientific tests. In this way the following materials were used and tested, infusion of turnip, of pounded cheese, hay, meat, fish, besides egg-albumen, blood, and urine. Vegetable productions, animal tissue, and secretions of the human body closely connected with vital processes, were thus subjected to test. In the history of investigation, attention ultimately concentrated on the infusion of hay and on urine. Observations were conducted in Paris and London; results were published from time to time; singular divergence became apparent in these recorded results; this led to controversy, which became so keen, that the Academy of Sciences in Paris appointed a commission of three to adjudicate upon a challenge given by M. Pasteur of Paris to Dr. Bastian of London; which Commission met in Paris on 15th July, 1877, but never adjudicated in the matter.[G] The perplexities encountered in conducting observations arose chiefly from two causes: the difficulty of ascertaining the temperature at which living organisms were certainly destroyed, and the materials sterilized; and that of guarding against interference with this state when established, by contact with the atmosphere. The latter perplexity, involving much care, skilful manipulation, and mechanical contrivance, was at last overcome by the construction of glass tubes, separating for a time the distinct materials, with facility for their mixture at the proper moment without contact with the air.