152 



MICRO-ORGANISMS AND FERMENTATION. 



Fermi and Montesano found that Bac. Megatherium, Proteus 

 vulgaris, and Bac, fluorescens liquefaciens in neutral broth, 

 invert a 4 per cent, solution of saccharose. Many of these 

 bacteria, however, loss their power of inversion if the broth 



Pig. 28. Bacillus subtilis. A, Cells with cilia ; B, C, segmented threads; D, thread with spores ; 

 E, spores in swollen mother-cell ; F, germination of spores ; G, film on hay infusion. 



is ^rendered alkaline, whilst most of them are uninjured in 

 slightly acid broth. In broth without sugar, and in media 

 containing no albumen, such bacteria pro- 

 duce invertase ; thus almost all the species 

 that were examined formed invertase in a 

 nutritive salt solution containing glycerine. 

 The invertase produced by these bacteria 

 proves to be a soluble enzyme, which is 

 destroyed at temperatures differing ac- 

 cording to the species, but it is always 



J 



more resistant during its action on sac- 

 charose than in a dissolved state ; it is very sensitive to acids 

 and alkalies, and especially to organic acids and potash. 



According to A. J. Brown, the well-known Bac. subtilis (hay 

 bacillus, Figs. 28 and 29), belongs to this group. Brown found 

 that it cannot grow either in beer or wort of normal acidity. 



According to Hansen, many species of bacteria of common 

 occurrence in beer secrete inverting ferments. Amongst these 



Fig. 29.- Bacillus 



(after A. Fischer). 



staining, x 1500. 



Cilia 



