GENERAL VIEW OF FERMENTATIVE ACTIVITIES 559 



the identification of the species employed by different authors correspondingly 

 difficult. Hence it is uncertain how far the following species studied by Beyerinck 

 are identical with those of other authors. According to Beyerinck, (i) Granulobacter 

 saccharobutyricum (anaerobe) is the common butyric bacterium which ferments sugar 

 producing butyric acid and also carbon dioxide, hydrogen, and a little butyl-alcohol. 

 It may be identical with Fitz's Bacillus butylicus, and allied to B. orthobutylicus. 

 (2) Granulobacter butylicum is also an anaerobe and forms in addition to carbon 

 dioxide and hydrogen, mainly butyl-alcohol, and a little butyric acid when fermenting 

 dextrose, but none from maltose. (3) Granulobacter lactobutylicum is able as an 

 anaerobic Clostridium form to ferment calcium lactate, forming calcium butyrate, 

 carbon dioxide, hydrogen, and a few by-products, but when exposed to air the 

 power of fermentation is lost and the calcium lactate is converted into carbonate 

 without any formation of butyric acid. When cultivated as an anaerobe this species 

 perishes after exciting a slight amount of fermentation, and hence it is possibly an 

 example of an organism in which an alternation from aerobiosis to anaerobiosis is 

 necessary for continued existence (Sect. 97). 



Lactic fermentation. As the result of the fermentation of various 

 sugars by different aerobic and anaerobic bacteria, lactic acid appears as 

 a main or by-product. Kayser 1 experimented with a large number of 

 lactic bacteria and found that under favourable circumstances 95 per cent, 

 of the sugar was converted into lactic acid (C 6 Hi 2 O 6 =2C 3 H 6 O 3 ), while 

 at the same time carbon dioxide and traces of acetic, formic acids, &c. 

 were produced. In very many cases but little carbon dioxide is formed, 

 and indeed it occasionally happens that no gaseous products at all appear 

 (Sect. 98). But little energy is derived from the direct lactic fermentation 

 of sugar, and hence the process may not be of primary importance in 

 the respiratory metabolism of lactic bacteria. Owing to the sensitiveness 

 of these to free acid the fermentative activity soon ceases unless chalk is 

 added, but the amount of acid which may accumulate varies according 

 to the species and the cultural conditions, both of which influence the 

 ratio between the main and by-products. A bacterium which normally 

 produces an optically inactive form of lactic acid may under different condi- 

 tions form an optically positive or optically negative variety of lactic acid 2 . 



Acetic fermentation. A small quantity of acetic acid is commonly 

 produced in both oxidative and disintegratory fermentations, and in the 

 oxidation of ethyl-alcohol by certain bacteria acetic acid is formed in abund- 

 ance. According to Lafar a certain form of yeast has the same power 3 . 

 These acetic bacteria, of which Hansen's researches have made Bacterium 



i Kayser, Ann. d. 1'Inst. Pasteur, 1894, T. vnr, p. 737- Cf. also Flugge, 1. c., p. 232 ; 

 1. c., p. 200, and the literature here given. 



* Cf. Pfeffer, Jahrb. f. wiss. Bot, 1895, Bd. xxvm, p. 226. 



' Lafar Centralbl. f. Bact., 1893, Bd. xill, p. 684. Cf. Fliigge, 1. c., p. 248 ; Lafar, 1. c., p. 343 1 

 Ad. Mayer, 1. c., p. 170; Henneberg, Centralbl. f. Bact , 1897, Abth. ii, Bd. m, p. 223. 



