of yeast had been formed, and that 45 grammes (693 grains) of sugar had fermented, the ratio between the weights of yeast and sugar being thus 0.255 divided by 45 = 1 divided by 176.  In this experiment the yeast developed with much difficulty, by reason of the conditions to which it had been subjected.  In appearance the cells varied much, some were to be found large, elongated, and of tubular aspect, some seemed very old and were extremely granular, whilst others were more transparent.  All of them might be considered abnormal cells.

In such experiments we encounter another difficulty.  If the yeast sown in the non-aerated fermentable liquid is in the least degree impure, especially if we use sweetened yeast-water, we may be sure that alcoholic fermentation will soon cease, if, indeed, it ever commences, and that accessory fermentations will go on.  The vibrios of butyric fermentation, for instance, will propagate with remarkable facility under these circumstances.  Clearly then, the purity of the yeast at the moment of impregnation, and the purity of the liquid in the funnel, are conditions indispensable to success.

To secure the latter of these conditions, we close the funnel, as shown in fig. 2, by means of a cork pierced with two holes, through one of which a short tube passes, to which a short length of india-rubber tubing provided with a glass stopper is attached; through the other hole a thin curved tube is passed.  Thus fitted, the funnel can answer the same purposes as our double-necked flasks.  A few cubic centimetres of sweetened yeast-water are put in it and boiled, so that the steam may destroy any germs adhering to the sides; and when cold the liquid is impregnated by means of a trace of pure yeast, introduced through the glass-stoppered tube.  If these precautions are neglected, it is scarcely possible to secure a successful fermentation in our flasks, because the yeast sown is immediately held in check by a development of anaerobian vibrios.  For greater security, we may add to the fermentable liquid, at the moment when it is prepared, a very small quantity of tartaric acid, which will prevent the development of butyric vibrios.

[Illustration with caption:  Fig. 4.]

The variation of the ratio between the weight of the yeast and that of the sugar decomposed by it now claims special attention.  Side by side with the experiments which we have just described, we conducted a third lot by means of the flask C (Fig. 4), holding 4.7 litres (8 1/2 pints), and fitted up like the usual two-necked flasks, with the object of freeing the fermentable liquid from foreign germs, by boiling it to begin with, so that we might carry on our work under conditions of purity.  The volume of yeast-water (containing 5 per cent. of sugar) was only 200 cc. (7 fl. oz.), and consequently, taking into account the capacity of the flask, It formed but a very thin layer at the bottom.  On the day after impregnation the deposit