BUTYRIC ACID BACTERIA 121 



is made both durable and more tasty for the cattle. Sauerkraut is another 

 foodstuff that is the result of such fermentation. In all these cases butyric 

 fermentation occurs at the same time. 



Butyric Fermentation (94). 



The butyric fermentation, a strictly anaerobic process, is no less widely 

 distributed in nature than the lactic. Its importance for the general theory 

 of fermentation will be considered in the next chapter. 



There are several means of obtaining rough, impure fermentations of 

 butyric bacteria from which, by growing in hydrogen or by other anaerobic 

 methods, pure cultures may be derived. It suffices to place some peas in 

 a saccharine nutritive fluid and close the culture flask with a cork through 

 which passes a tube whose outer end dips under water. In a few days at 30 

 or 40 active fermentation sets in, large quantities of gas are given off, and 

 an odour of butyric acid is apparent. Another method is to boil a mixture of 

 5 grm. grape sugar and 5 grm. powdered fibrin in 100 c.c. water, and in- 

 oculate the liquid, whilst boiling, with a little garden earth. After forty-eight 

 hours at 35 the fermentative process is going on rapidly, and is caused 

 almost entirely by one species of bacterium, the Granulobacter saccharo- 

 butyricus of Beyerinck. 



Just as was the case with the lactic fermentation, the butyric fermenta- 

 tion was supposed formerly to be the work of one species of micro-organism 

 only, the Vibrion butyrique of Pasteur (A mylobacter butyrictts, van Tieghem). 

 There can be no doubt, however, that these terms have both morpho- 

 logically and physiologically only the value of collective designations, as is 

 the case with the Clostridium btityricum of Prazmowski. Some twenty 

 different forms of butyric bacteria have been more or less precisely de- 

 scribed, and the number could be probably reduced to two or three. Many 

 are distinguished by the granulose reaction (Beyerinck's biological genus 

 Granulobacter}, and some are characterized by the alteration in shape of 

 the cell during sporulation, a process which sets in with great regularity 

 towards the end of fermentation (Fig. 24, e, f). The commonest form of 

 the spore-bearing cell is the spindle shape (Clostridium\ but some species 

 swell at the end (drum-stick, Plectridium). Almost all are comparatively 

 large cells (0-5-1 /u. by 3-1 OJM) actively motile and peritrichous (Fig. 24, e,f). 



Granulobacter saccharobutyricus and G. lactobutyricus (anaerobic Clos- 

 tridia with granulose), and Bacilhis orthobutylicus (an anaerobic Clostridium 

 with no granulose), all produce considerable quantities of butyric acid, with 

 some CO 2 , free hydrogen, acetic, and traces of other fatty acids. B. ortho- 

 butylicus ferments carbohydrates and other compounds of many different 

 kinds ; glycerine, mannite, glucose, cuvert-sugar, cane-sugar, maltose, lactose, 

 arabinose, starch, dextrine, inuline (not trehalose), erythrite, and gum arabic. 



