60 



MICRO-ORGANISMS AND FERMENTATION. 



Whilst PASTEUR, in the work mentioned above, does not 

 explicitly maintain the theory that the oxidation of alcohol 

 to acetic acid, brought about by acetic acid bacteria, is a 

 purely physiological process, ADOLF MAYER expresses this 

 opinion, the correctness of which he has confirmed. HANSEX 

 also emphasises as a certainty the fact that the formation 

 of acetic acid is commonly effected by the action of bacteria. 

 PASTEUR showed that the acetic acid generated by the oxidation 

 of ethyl alcohol is transformed, if the oxidation is continued, 

 into carbon dioxide and water. This was recently confirmed 

 by ADRIAN J. BROWN, to whom we owe the most thorough 

 investigations into the chemical effects of acetic acid bacteria. 



HANSEN'S researches are among the first which proved that a 

 definite fermentation is not induced by one species of bacterium 

 only, but by several ; these researches also furnish some of the 

 earliest experimental evidence of the fact that one and the same 

 species can occur in very different shapes ; the correctness of 

 his results was later confirmed by ZOPF, DE BARY, and A. J. 

 BROWN. By means of his staining experiments with Bad. 

 (Mycoderma) aceti (1879), he discovered that at least two 

 distinct species are hidden under this name, of which the one, 

 like most other bacteria, is stained yellow by iodine, whilst the 

 other assumes a blue coloration with the same reagent. For 



the former he retained the old name 

 Bad. aceti, whilst the one stained blue 

 he named after PASTEUR B. Pasteur- 

 ianum. The film formations on wort 

 and beer, and likewise the growths on 

 wort-gelatine, give a fine blue colour 

 with tincture of iodine, or iodine 

 dissolved in a solution of potassium 

 iodide, whilst the growths which develop 

 on yeast-water and meat-decoction with 

 peptone and gelatine are coloured 

 yellow ; even very old films on beer 



show a yellow reaction. It is the gelatinous formation 

 secreted from the cell-wall that is coloured blue. HANSEN 

 discovered a third species at a later period. 



Fio. 14. Bacterium aceti. (After 

 HANSEN.) 



