GENERAL VIEW OF FERMENTATIVE ACTIVITIES 557 



decreases. Chudiakow supposes that in the latter case the change in the nutritive 

 conditions operates injuriously and thus inhibits fermentation, but since growth 

 continues it is possible that the stoppage is produced in the same manner as in 

 the case of Mucor. It is well known that certain bacteria grow or die in the 

 presence of air according to the cultural conditions. Rapp ' was unable to confirm 

 Chudiakow's results; he also observed that strong agitation diminishes the fermen- 

 tative activity of yeast. Hence Chudiakow's results can only be explained by 

 supposing that the sensitiveness of yeast to agitation, such as is caused by the 

 passage of streams of air-bubbles, varies according to the culture-medium. 



The activity of fermentation depends upon the supply of sugar, the 

 multiplication of the yeast-cells, the accumulation of the products, the 

 temperature, &c. (Sect. 104). The most actively fermenting yeasts with- 

 stand percentages of alcohol which are fatal to most plants, for alcohol 

 may accumulate in a fermenting liquid to the extent of 14 per cent, by 

 volume, although the growth of the yeast is checked when 12 per cent, is 

 reached 2 . Hansen found that with Mncor erectiis and M. racemosus as 

 much as 8 per cent, might accumulate, but in the case of Mrtcor mucedo 

 the culture fluid only contained 3 per cent, of alcohol after three months 

 activity 3 . Hence many seedlings and fruits exhibit a more marked 

 production of alcohol in the absence of oxygen than Mncor mucedo does 

 (Sect. 99). 



Even the best yeasts use 5 to 6 per cent, of the sugar in producing 

 glycerine, succinic acid, acetic acid, and small quantities of other substances, 

 both the absolute and relative amounts of which vary during the progress 

 of fermentation and according to the external conditions. Many plants 

 form in addition to alcohol large quantities of other substances, and in 

 certain bacterial fermentations ethyl-alcohol appears only as a by-product. 

 As a general rule the amount of by-products produced by yeast increases 

 under unfavourable conditions, but at 30 C. Nageli 4 found that beer-yeast 

 was able to ferment forty times its own dry weight of cane-sugar in 

 twenty-four hours, and that almost the whole of this sugar underwent 

 alcoholic fermentation. 



A similar fermentative activity does not indicate any systematic rela- 

 tionship between plants. This statement applies to the yeast-like growths 

 formed by certain fungi under conditions which excite fermentative activity 5 . 



1 Rapp, Ber. d. Chem. Ges., 1896, p. 1983. 



8 Cf. Kayser, Jahresb. d. Gahrungsorg., 1892, p. 1 14 ; Wortmann, Landw. Jahrb., 1894, Bd. XXIII, 

 pp. 548, 555. 



3 Hansea, Meddelelser f. Carlsberg Laboratories 1882, Bd. 11, p. 160; Brefeld, Landw. Jahrb., 

 1876, Bd. v, p. 305; Pasteur, tude s. 1. biere, 1876, p. 133; Lesage, Ann. d. sci. nat, 1897, 

 vii. sen, T. in, p. 151. 



* Nageli, 1. c., p. 32. See also Giltay u. Aberson, 1. c., 1894, p. 560. 



5 Cf. Klebs, Die Bedingnngen d. Fortpflanzung, &c., 1896, p. 509; Schostakowitsch, Flora, 

 Erg.-bd., 1895, pp. 371, 391. 



