of yeast was already considerable, and forty-eight hours afterwards the fermentation was completed.  On the third day we collected the yeast after having analyzed the gas contained in the flask.  This analysis was easily accomplished by placing the flask in a hot-water bath, whilst the end of the curved tube was plunged under a cylinder of mercury.  The gas contained 41.4 per cent. of carbonic acid, and, after the absorption, the remaining air contained:—­

Oxygen . ... . ... . ... . ... . ... . ... . ... ... 19.7

Nitrogen . ... . ... . ... . ... . ... . ... . ... . 80.3

100.0

Taking into consideration the volume of this flask, this shows a minimum of 50 cc. (3.05 cub. in.) of oxygen to have been absorbed by the yeast.  The liquid contained no more sugar, and the weight of the yeast, dried at a temperature of 100 degrees C (212 degrees F.), was 0.44 grammes.  The ratio between the weights of yeast and sugar is 0.44/10=1/22.7 [Footnote:  200 cc. of liquid were used, which, as containing 3 per cent., had in solution 10 grammes of sugar.—­D.C.R.].  On this occasion, where we had increased the quantity of oxygen held in solution, so as to yield itself for assimilation at the beginning and during the earlier developments of the yeast, we found instead of the previous ratio of 1/76 that of 1/23.

[Illustration with caption:  Fig. 5]

The next experiment was to increase the proportion of oxygen to a still greater extent, by rendering the diffusion of gas a more easy matter than in a flask, the air in which is in a state of perfect quiescence.  Such a state of matters hinders the supply of oxygen, inasmuch as the carbonic acid, as soon as it is liberated, at once forms an immovable layer on the surface of the liquid, and so separates off the oxygen.  To effect the purpose of our present experiment, we used flat basins having glass bottoms and low sides, also of glass, in which the depth of the liquid is not more than a few millimetres (less than 1/4 inch) (Fig. 5).  The following is one of our experiments so conducted:—­On April 16th, 1860, we sowed a trace of beer yeast ("high” yeast) in 200 cc. (7 fl. oz.) of a saccharine liquid containing 1.720 grammes (26.2 grains) of sugar-candy.  From April 18th our yeast was in good condition and well developed.  We collected it, after having added to the liquid a few drops of concentrated sulphuric acid, with the object of checking the fermentation to a great extent, and facilitating filtration.  The sugar remaining in the filtered liquid, determined by Fehling’s solution, showed that 1.04 grammes (16 grains) of sugar had disappeared.  The weight of the yeast, dried at 100 degrees C. (212 degrees F.), was 0.127 gramme (2 grains), which gives us the ratio between the weight of the yeast and that of the fermented sugar 0.123/1.04=1/8.1, which is considerably higher than the preceding ones.