The following experiments were undertaken to solve this double problem:—­We took a double-necked flask, of three litres (five pints) capacity, one of the tubes being curved and forming an escape for the gas; the other one, on the right hand side (Fig. 1), being furnished with a glass tap.  We filled this flask with pure yeast water, sweetened with 5 per cent, of sugar candy, the flask being so full that there was not the least trace of air remaining above the tap or in the escape tube; this artificial wort had, however, been itself aerated.  The curved tube was plunged in a porcelain vessel full of mercury, resting on a firm support.  In the small cylindrical funnel above the tap, the capacity of which was from 10 cc. to 15 cc. (about half a fluid ounce) we caused to ferment, at a temperature of 20 degrees or 25 degrees C. (about 75 degrees F.), five or six cubic centimetres of the saccharine liquid, by means of a trace of yeast, which multiplied rapidly, causing fermentation, and forming a slight deposit of yeast at the bottom of the funnel above the tap.  We then opened the tap, and some of the liquid in the funnel entered the flask, carrying with it the small deposit of yeast, which was sufficient to impregnate the saccharine liquid contained in the flask.  In this manner it is possible to introduce as small a quantity of yeast as we wish, a quantity the weight of which, we may say, is hardly appreciable.  The yeast sown multiplies rapidly and produces fermentation, the carbonic gas from which is expelled into the mercury.  In less than twelve days all the sugar had disappeared, and the fermentation had finished.  There was a sensible deposit of yeast adhering to the sides of the flask; collected and dried it weighed 2.25 grammes (34 grains).  It is evident that in this experiment the total amount of yeast formed, if it required oxygen to enable it to live, could not have absorbed, at most, more than the volume which was originally held in solution in the saccharine liquid, when that was exposed to the air before being introduced into the flask.

[Illustration with caption:  Fig. 1]

Some exact experiments conducted by M. Raulin in our laboratory have established the fact that saccharine worts, like water, soon become saturated when shaken briskly with an excess of air, and also that they always take into solution a little less air than saturated pure water contains under the same conditions of temperature and pressure.  At a temperature of 25 degrees C. (77 degrees F.), therefore, if we adopt the coefficient of the solubility of oxygen in water given in Bunsen’s tables, we find that 1 litre (1 3/4 pints) of water saturated with air contains 5.5 cc. (0.3 cubic inch) of oxygen.  The three litres of yeast-water in the flask, supposing it to have been saturated, contains less than 16.5 cc. (1 cubic inch) of oxygen, or, in weight, less than 23 milligrammes (0.35 grains).  This was the maximum amount of oxygen, supposing the