BACTERIA. 59 



researches are, moreover, among the first which proved that a 

 definite fermentation is not induced by one species of 

 bacterium only, but by several ; more recently a large number 

 of instances have been discovered. By placing lager-beer in 

 an incubator at 30 to 34 C., he obtained a vigorous film- 

 growth of the acetic-acid bacterium. This consists of long 

 chains of hour-glass-like members, partly as bacterium and 

 bacillus, partly as wavy or curved forms. As a peculiarity 

 of Bad. aceti it may be mentioned that this species often 

 yields at a very early stage the different, irregularly swollen 

 involution forms above described, whilst other bacteria do not 

 produce these forms until a very advanced stage, and even 

 then, possibly, only as a consequence of a deficient supply of 

 nutriment; this, however, cannot be the case with the 

 organism under discussion. We have here also one of the 

 first cases, in which it has been shown that the same species 

 can occur in very different forms. 



By means of his staining experiments with Bact. aceti, 

 Hansen discovered, as already stated, that 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 retains the old name Bact. aceti, whilst the one 

 stained blue he names after Pasteur B. Pasteurianum. In 

 a lecture he communicated the following new observations : 

 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 iodide of potassium, 

 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 ; it has hitherto not been possible to determine 

 whether the contents of the cells are coloured or not. In 

 wort-gelatine, Bact. Pasteurianum develops round specks or 

 colonies with a smooth or wavy border, whilst the corresponding 



