380 STUDIES ON FERMENTATION. 



similar phenomenoii is observable in the case of wort. After 

 having acquired a marked dark shade by remaining in contact 

 with pure air, it loses this colour very appreciably during 

 fermentation ; and if the wort does not quite regain the 

 colour which it originally had when it came from the copper, 

 this circumstance is probabh' owing to the fact that the quan- 

 tity of oxygen in combination with the wort is larger than that 

 which is abstracted b}^ the yeast. We have seen that yeast 

 absorbs oxygen, since, in the case of a saccharine wort, more or 

 less saturated with oxygen in solution, when fermentation com- 

 mences, the first efiect of the ferment is to cause that oxygen 

 to combine with its own substance. We should, therefore, 

 expect to find the oxygen in combination, as well as that held 

 in solution, in wort, abstracted by the yeast and contributing 

 to the activity of fermentation. As a matter of fact, this is 

 proved by direct experiments, for the fermentation of a wort 

 that has oxidized in contact with air, or of one from which all 

 the oxygen that was held in solution in it has disappeared by 

 direct combination, is much more easy, rapid, and complete than 

 the fermentation of the same wort when it contains no oxygen, 

 whether free or combined. These experiments were as follows : 

 we boiled some copper wort in a large double-necked flask, like 

 those shown in Fig. 73 : all the air being expelled, pure air 

 was allowed to enter the flask ; and when the wort was cool it 

 was saturated with this air, by being shaken briskly for a 

 quarter of an hour. The wort was then forced by a pressure of 

 air, applied to the extremity of the S-shaped tube, into smaller 

 flasks, similar to the preceding ones ; these we filled completely, 

 and then plunged the end of their sinuous tubes under mercury. 

 After waiting for two or three days, a longer time than was 

 required for the oxj-gen in solution to enter into combination — 

 a fact which we confirmed by means of a similar flask, whicli 

 served as a standard — we caused the wort, so prepared, to fer- 

 ment in the flasks, and side by side, for the sake of comparison, 

 some copper u-ort that contained no air in solution or combination. 

 In other experiments we operated on pure wort, saturated 



