For these observations, we employed small glass cells, which we made out of some St. Gobain glass by punching holes through it, and then cementing on one side one of the little glasses used for covering objects in microscopical examinations. In this manner we made small troughs, in which we placed some wort that had been boiled, and a drop of the water in which grapes had been washed. To prevent evaporation we covered the cells with a sheet of glass. We examined the liquid in these cells by inclining our microscope to the angle required.[88] [Illustration: Fig. 29.] We also made use of cells similar to those employed by MM. Van Tieghem and Lemonnier[89] in their researches on _mucorines_ (Fig. 30). [Illustration: Fig. 30.] An apparatus similar to that employed by M. Duclaux in 1853[90] would do equally well. We should be able to work with even greater facility if we employed bulbs like some which we ordered in Germany, some twelve years ago, of the well-known glass-blower, Geissler. We have heard that these bulbs now sold by that maker are much used by German microscopists. They consist of a tube blown out into a flat bulb, the sides of which, in the centre, come sufficiently close together to enclose but a very thin layer of liquid, and to admit of microscopical examination. We may fill these tube-bulbs completely with liquid, to the exclusion of air or we may surround the central drop with air. [Illustration: Fig. 31.] Footnote 88: In our essay on acetic fermentation, published in 1864, we have already described this apparatus, which we employed to follow the multiplication of the jointed filaments of _mycoderma aceti_. See PASTEUR, _Etudes sur le vinaigre_, p. 64, Paris, 1868. Footnote 89: VAN TIEGHEM and LEMONNIER, _Annales des Sciences naturelles_, 5th series, _Botanique_, t. xvii. 1873. Footnote 90: DUCLAUX, _Comptes rendus des séances de l’Académie des Sciences_, t. lvi. p. 1225. Footnote 91: In experiments of this kind there is always a slight increase in the volume of air in the jar. This increase may be very perceptible even when the experiment made with fresh grapes, in August, for instance, causes no fermentation due to the action of yeast. After the oxygen of the air has been absorbed and replaced by carbonic acid gas, either by direct oxidation or by the action of moulds, the grapes, although crushed, act like fruits plunged into carbonic acid gas[92], and this effect is even more marked in the case of imperfectly crushed grapes. The reason is, that the crushing is never so perfect as to injure all the cells of the parenchyma. We may easily convince ourselves that the experiment on the liberation of carbonic acid gas and the formation of alcohol by grapes and fruits in general when plunged into carbonic acid succeeds very well in the case of fragments of fruits or grapes, and succeeds better the less the parts are crushed.