A practical conclusion from these experiments is that a high [p035] concentration of sugar tends to preserve the enzyme in an active state for a longer time. Simultaneously it prevents the development of bacteria and yeast cells.
(f) Effect of Varying Concentration of Yeast-Juice.
This subject, which is of considerable importance with reference to the question of the protoplasmic or enzymic nature of the active agent in yeast-juice, has been examined in some detail by Buchner [Buchner, E. and H., and Hahn, [1903], pp. 158–65] and by Meisenheimer [[1903]] for juices from bottom yeast, by Harden and Young [[1904]] for those from top yeast, and by Lebedeff [[1911, 4]] for maceration extract, the results obtained being in substantial agreement.
Dilution of yeast-juice with sugar solution, so that the concentration of the sugar remains constant, produces a small progressive diminution in the total fermentation, which only becomes marked when more than 2 volumes are added, and this independently of the actual concentration of the sugar. Dilution with water produces a somewhat more decided diminution, which, however, does not exceed 50 per cent. of the total for the addition of 3 volumes of water. The effect on maceration extract is somewhat greater but of the same kind. The autofermentation of juice from top yeast is scarcely affected by dilution with 4 volumes of water.
| Nature of Juice. | Per cent. of Sugar Employed by Weight. | Volumes of Sugar Solution Added. | Volumes of Water Added. | Total Fermentation in g. of CO2. | |
|---|---|---|---|---|---|
| Bottom Yeast | 1 | 29 | 0 | — | 0·99 |
| 1 | — | 1·13 | |||
| 2 | — | 0·92 | |||
| 4 | — | 0·79 | |||
| 2 | 9 | 0 | — | 0·43 | |
| 1 | — | 0·60 | |||
| 2 | — | 0·53 | |||
| 4 | — | 0·41 | |||
| 3 | 9 | — | 0 | 0·46 | |
| — | 1 | 0·32 | |||
| — | 2 | 0·33 | |||
| — | 3 | 0·36 | |||
| Top Yeast | 1 | 0 (Auto- ferment- ation) | — | 0 | 0·29 |
| — | 2 | 0·29 | |||
| — | 3 | 0·28 | |||
| 2 | 29 | 0 | — | 0·31 | |
| 1 | — | 0·34 | |||
| 2 | — | 0·31 | |||
| 4 | — | 0·35 | |||
| 6 | — | 0·28 | |||
| 3 | 7·4 | — | 0 | 0·44 | |
| — | 1 | 0·35 | |||
| — | 2 | 0·30 | |||
| — | 3 | 0·28 | |||
On the whole, therefore, yeast-juice may be said to be only slightly affected by dilution even with pure water, and the effect of the latter can in no way be regarded as comparable with the poisonous effect which it exerts on living protoplasm, as suggested by Macfadyen, Morris, and Rowland [[1900]].
(g) The Effect of Antiseptics on the Fermentation of Sugars by Yeast-Juice.
Buchner has paid special attention to the effect of antiseptics on the course of fermentation by yeast-juice [Buchner and Rapp, [1897]; [1898, 2], [3]; [1899, 1]; Buchner and Antoni, [1905, 1]; Buchner and Hoffmann, [1907]; Buchner, E. and H., and Hahn, [1903], pp. 169–205; see also Albert, [1899, 2]; Gromoff and Grigorieff, [1904]; Duchaček, [1909]] in order (1) to obtain evidence as to the possibility of the active agent in yeast-juice consisting of fragments of protoplasm and not of a soluble enzyme, and (2) also to provide a safe method of avoiding contamination, by the growth of bacteria or yeasts, of the liquids used which were often kept at 25° for several days. The results of these experiments are briefly summarised in the following table, in which the effect of each substance on the total fermentation produced is noted:—
| Substance. | Effect on Total Fermentation. | |
|---|---|---|
| Concentrated solution of glycerol | Slight diminution | |
| Concentrated solution of sugar | Slight increase | |
| Toluene (to saturation or excess) | Less than 10 per cent. diminution | |
| Chloroform | 0·5 per cent. | Slight increase |
| 0·8 per cent. (saturation) | No change | |
| Large excess (17 per cent.) | 64 per cent. diminution | |
| Chloral hydrate | 0·7 per cent. | Increase up to 27 per cent. |
| 3·5–5·4 per cent. | Completely destroyed | |
| Phenol | 0·1 per cent. | No change |
| 0·5 " | 40 per cent. diminution | |
| 1·2 " | Completely destroyed | |
| Thymol | 1 " | Slight diminution |
| 5 " | Marked " | |
| Benzoic acid | 0·1 " | 7 per cent. diminution |
| 0·25 " | 26 " | |
| Salicylic acid | 0·1 " | 10 " |
| 0·27 " | 35 " | |
| Formaldehyde | 0·12 " | 20 " |
| 0·24 " | 30–60 " | |
| Acetone | 6 " | 20 " |
| 14 " | 80 " | |
| Alcohol | 6 " | 0–20 " |
| 14 " | 75 " | |
| Sodium fluoride | 0·5 " | 90 " |
| 2 " | Almost completely destroyed | |
| Ammonium fluoride | 0·55 per cent. | Completely destroyed |
| Sodium azoimide, NaN3, | 0·36 per cent. | Slight diminution |
| 0·71 " | Marked " | |
| Quinine hydrochloride | 1 " | Slight increase |
| Ozone | 10·4–34·8 mgs. per 20 c.c. | Marked diminution |
| Hydrocyanic acid | 1·2 per cent. | Completely destroyed |