A remarkable fact in this fermentation is the evolution of free N, which seems to be rare, except in the case of putrefactive organisms, as in the vast number of fermentative decompositions due to bacteria, almost the only gases found are carbonic anhydride, hydrogen, H_{2}S, and marsh gas. Gayon[182] in 1875, in an investigation on the putrefaction of eggs, collected the gas given off from large ostrich eggs, and found in it 29 per cent. of nitrogen; he adds, however, that its presence may be due to the accumulation of a certain quantity of air in the air-bubble before putrefaction. [182] Schutzenberger, “Fermentation,” 1876, p. 227. Béchamp[183] found that yeast cells under suitable conditions, but sugar being withheld, produced pure nitrogen along with leucin, tyrosin, a soluble albuminous substance coagulable by heat, an enzyme, a peculiar gummy substance, phosphates and acetic acid, alcohol and CO_{2}. These are almost the only instances where observers of repute have been convinced of the evolution of free N by bacteria. We find since the above work was carried out that Immendorf[184] has found certain bacteria in dung which form ammonium nitrate, and this body, as is known, splits up at a comparatively low temperature into nitrogen and water. [183] Woodhead, “Bacteria and their Products,” p. 125. [184] Die Stickstoffkonservirung im Stalldünger, Jour. f. Landwirthsh., xlii. p. 69. From the bacteriological as well as the chemical results, it is now evident that the fermentation as it takes place in practice is a symbiotic one in which two organisms play the most important part, and very probably cause the entire fermentation. This is shown by comparing the acids produced by the fermentation in the works with those produced by a mixture of the organisms α and β, the relative amounts being very close, while in all the fermentations with α alone a much less proportion of lactic acid is produced, as the following table shows:-- -----------+------------+------------+------------+------------ -- |Fermentation|Fermentation|Fermentation|Fermentation | in Works | α and β | α (II.) | α (III.) -----------+------------+------------+------------+------------ Formic acid| 2·8 | 0·8 | 11·8 | 16·0 Acetic " | 22·5 | 16·4 | 27·9 | 22·7 Butyric " | 1·2 | 4·5 | 3·5 | 0·9 Lactic " | 73·5 | 78·3 | 56·7 | 60·2 -----------+------------+------------+------------+------------ NOTE.--Ruge (Sitzungsber. d. Wien. Akad. d. Wiss, Vol. xliv., 1862, 734) found that the gases of the large intestine contained 57·8 per cent. of N, and Gamgee remarks “in part a diffusate from the blood, but is certainly in part derived from the bacterial decomposition of proteids.” (Gamgee, Phys. Chem. Vol. ii., p. 467.)