CONSUMPTION OF OXYGEN. 



231 



fermentation barm per hectolitre respectively. The results are 

 expressed in the following table, which shows, in the first place, 

 the total crop from each sowing, and then the actual increase 

 (crop minus sowing) : 



It is thus evident that while an increase in the amount of the 

 sowing has little effect on the total crop, it causes an appreciable 

 diminution of the increase. This fact has been repeatedly con- 

 firmed : for instance, by O. E.IENKE (II.) in 1889 for low-fermen- 

 tation beer yeast; by A. J. BROWN (VII. and IV.) in 1890 and 

 1892 for Burton top-fermentation yeast; in 1897 by Thausing 

 himself in new experiments ; and in the same year by A. 

 REICHARD and A. RIEHL (II.) at the low-fermentation brewery 

 at Lutterbach (Elsass), and by the BIERBROUWERY D'ORANJEBOOM 

 (I.) at Rotterdam. 



The latter also confirmed Thausing's discovery that the 

 accuracy of the results is unaffected by the height of the 

 temperature, it being immaterial whether the fermentation was 

 conducted at a low temperature (starting at 3.8 C. and rising to 

 9.4 C., to afterwards recede to 6 C.), or in the warm, com- 

 mencing at 10. i C., rising to above 15.8 C., and afterwards 

 declining to 10 C., or finally carried on at the usual level of 

 8 0., 8.8 C., and 11 C. In low-fermentation breweries it is 

 customary to pitch the wort with J per cent, by volume of thick 

 barm, which increases about eightfold during fermentation. 

 The resulting deposit of yeast at the bottom of the fermentation 

 vessel consists of three layers : bottom, middle or core, and top, 

 the middle one being carefully separated from the other two and 

 alone used for pitching subsequent brews. It forms about 60 

 per cent, of the total deposit, but suffers diminution during the 

 washing process to which it is subjected, the final yield being 

 only about twice the original amount of the pitching yeast. 



266. Consumption of Oxygen for Cell Reproduction 

 and Respiration, 



The question whether strictly anaerobic species of yeast (see 

 vol. i. p. 181) exist, and therefore whether cell reproduction 

 can proceed, without restriction, in the entire absence of free 



