Oxygen then presents itself to us as being endowed with a certain determining stimulus in the matter of nutritive action enabling this action to be prolonged beyond the point where the direct influence of oxygen ceases. In time the energy that has been imparted to the cells will die away, and then also fermentation will cease, to be resumed, however, when the plant is once more submitted to the revivifying action of the gas. It seems as though the vital energy derived from the influence of gaseous oxygen were capable of effecting an assimilation of oxygen, not in the gaseous state, but existing in some state of combination, and hence its power of causing the decomposition of sugar. Looking at the matter in this light, it seems to us that we may discover in it a fact of general occurrence, that this peculiar action of the oxygen and the cells is to be seen in all living beings. For indeed is there any cell which, if suddenly and completely deprived of air, would perish forthwith, and absolutely? Probably there is not a single one that would do so. With certain modifications of greater or less amount the assimilative and excretive acts which have taken place during life must be carried on after the suppression of oxygen, resulting in fermentations ordinarily obscure and feeble, but in the case of the cells of ferments, properly so called, manifesting an activity both greater in amount and more enduring. Let us now proceed to compare the weight of alcohol formed by the _mucor_ during fermentation with the weight of the plant itself. _First experiment._—One of the double-necked flasks contained at starting 120 c.c. (about 4 fl. oz.) of wort. On January 2nd, 1873, we attached this flask to a test-glass, containing a deposit of _mucor_ ferment (Fig. 19, p. 101), a few drops of which we poured into the wort in the flask, to impregnate it. On January 3rd we decanted the wort from the flask into the test-glass; under these conditions we have seen that the wort must ferment. On January 18th the fermentation in the test-glass ceased. On July 31st, 1873, we transferred the liquid from the test-glass back to the flask. On August 4th, 1873, we again decanted this same liquid from the flask into the test-glass. On December 25th, 1873, we once more removed the liquid from the test-glass to the flask, and allowed it to remain so until December 23rd, 1874, on which day we submitted it to examination. It was found to contain per 100 c.c. (3-½ fl. oz.) Grains. Grammes.[78] Total weight of the fungus 5·7 0·37 Absolute alcohol 50·9 3·3 Acidity, estimated in its equivalent of 1·7 0·11 sulphuric acid Sugar, determined by cupric solution 82·2 5·2 Dextrine (?) 24·6 1·6