Nearly the same results were obtained in the case of urine; it underwent no radical change; its colour merely assumed a reddish brown tint; it formed some small deposits of crystals, but without becoming at all turbid or putrefying in any way. The direct oxidation of the urinary substances was likewise very sluggish. An analysis of the air in one of the flasks, made forty days after the commencement of the experiment, gave the following results:— Oxygen 19·2 Carbonic acid 0·8 Nitrogen 80·0 ——- 100·0 These experiments on blood and urine which we have just mentioned date from 1863.[30] Ten years afterwards, in 1873, they were confirmed in an important and striking manner by the results of a very able series of experiments, which were carried out in our laboratory, by M. Gayon, who was formerly a pupil in the _École Normale Supérieure_. M. Gayon proved that what held good in the case of blood and urine, also held good in the case of the substances contained in eggs. He found that the whites of eggs might be exposed for any length of time to contact with air, as also might the yolks, or the white and yolks mixed, without any putrefactive change or fermentation resulting, and without the smallest microscopic germ showing itself, the sole condition being that the air must be freed from all organic particles of dust, germs of mould, _bacteria_, _vibrios_, and other organisms which it holds in suspension. This was only a part of the important facts brought to light by M. Gayon. Amongst other things, he proved that spontaneous putrefaction in eggs is invariably caused by the development of organized ferments, thereby correcting the opposite statements announced by M. Donné and M. Béchamp, who were led by their observations to believe that the change in eggs took place quite independently of the action of _vibrios_ and _mucedines_.[31] It is almost superfluous to remark how greatly the results of these experiments on blood, urine, and the components of the egg are opposed to the doctrine of spontaneous generation, as also to most modern theories on the generation of ferments. As long as experiments relating to the question of so-called _spontaneous_ generation were made on heated substances, the advocates of _heterogenesis_ had some grounds for asserting that such materials could not satisfy the conditions of spontaneous life, and that we should obtain different results by using natural organic liquids, which, if exposed to contact of pure air would doubtless serve for the production of new beings which did not issue from parents which resembled them. This novel enunciation of the hypothesis of spontaneous generation, the only one, we think, that could be defended after the publication of our Memoir, in 1862, is condemned by the preceding facts.