It is a very easy matter to study the liquids and growths in our flasks during the course of a single experiment. We take out the glass stopper that closes the india-rubber tube on the straight-neck, and, by means of a long rod or a glass tube previously passed through the flame, take up a quantity, which we draw out immediately for microscopical examination. We then replace the glass stopper, taking care to pass it through the flame before doing so, to burn up any organic particles of dust that it may have picked up from the table on which we laid it. Footnote 67: We may prove the occurrence of alcoholic fermentation by the cells of submerged _mycoderma vini_ in a different manner. To do this, after having made all our preparations as before and shaken up the film of _mycoderma vini_ in its liquid, we must attach our flask to a test flask (Fig. 19), and pass the turbid liquid into the latter. On succeeding days we shall detect a very protracted fermentation in the test flask; there will be a succession of minute bubbles rising from the bottom, but in small number at a time. The fermentation is very evident whilst it lasts, but is rather sluggish, and, although of very long duration, ceases long before the sugar is exhausted. This experiment proves better than any other the non-transformation of _mycoderma vini_ into other ordinary fungoid growths. For after decanting the liquid into the test flasks, the sides of the experimental flask remain covered with streaks of _mycoderma vini_ along with some of the liquid. Moreover, the flask is refilled with air, and this air is being constantly renewed, in part, by variations of the temperature of the oven, so that the _mycoderma_ remaining on the sides is thus placed under the most favourable conditions for transformation into other fungoid growths, if that were possible. It is still more easy to detach the experimental from the test flask, and to pass pure air into it, once or twice a day, or constantly. In any case, we shall never see anything besides the _mycoderma vini_ spring up within it. Footnote 68: See PASTEUR, _Comptes rendus des Séances de l’Académie des Sciences_, t. liv., 1862, and t. lv., 1862. _Études sur les Mycodermes, &c._ Footnote 69: In a subsequent chapter we shall prove that yeast is likewise incapable of transformation into _mycoderma vini_. Footnote 70: We secured the purity of our mycoderma by the same means that we have already described for the procuring of spores of _penicillium_ or other fungoid growths in a state of purity. Footnote 71: