The insoluble residue was dried at 110° C. till the weight was constant.
The total weight of calcium salts obtained was 0·7661 grm. (from 4/5 litre of drench), of which 0·5493 grm. yielded on ignition 0·1398 grm. CaO = 25·45 per cent. Theory requires for calcium lactate (C3H5O3)2Ca = 25·69 per cent. CaO.
0·7661 grm. calcium lactate in the quantity used = 0·9576 grm. per litre = 0·7907 grm. lactic acid per litre. The difference between this and the preceding amount of lactic acid found by titration, viz. 0·0426 grm., is probably accounted for by the presence of a small quantity of salts of lactic acid in the drench.
The second part of the subject which we proposed to consider was “In what way does the ferment act on the bran and on the skins?” The average composition of bran is shown in the following table:—
| Per Cent. | |
| Water. | 14 |
| Fibrin, etc. | 15 |
| Starch | 44 |
| Fat | 4 |
| Lignose and cellulose | 17 |
| Ash | 6 |
It will be seen, as stated in the former communication,[167] that the starch must be the principal body acted upon; but the cellulose is also an important constituent, and before going further it was necessary to ascertain if it took part in the fermentation. For this purpose some pure cellulose was prepared from cotton wool in the usual way, and small portions placed in tubes containing yeast-water[168] as a nutrient material. These were sterilised by steaming; two tubes were inoculated from a pure cultivation of the bacteria obtained in 1889, two were inoculated from an actual drench, and three left uninoculated; all of them were placed on the incubator at a temperature of 30°–33°. On the second day the inoculated tubes were cloudy, but no gas was given off, nor was any acid formed; in 10 days the cellulose had not disappeared, nor on examination with the microscope could any action be detected. The experiment was repeated with peptone as a nutrient medium, but with the same result. The conclusion is that the bacterium does not attack the cellulose, which thus takes no part in the fermentation. The starch and nitrogenous bodies of the bran are therefore the only bodies acted upon by the bacteria in this fermentation.
From the fact that bran drenches ferment in the same way when mashed at all temperatures from 20° C. to 40° C., and that in all cases the starch is decomposed, it was supposed that the ferment was capable of attacking the starch in its undissolved condition. To ascertain if this were so, it was necessary to use pure cultivations in the laboratory.
The usual methods employed had thrown no light on this part of the subject, as in order to sterilise the solutions they had been repeatedly boiled, and were thus not comparable with the fermentation as it takes place in the works.
In order to get rid of this difficulty, the starch was sterilised in a dry condition in the hot-air oven, by heating for several hours on successive days to 110° C.