386 MICRO-ORGANISMS AND FERMENTATION. 



product. Among the species examined many possess an 

 inverting enzyme. It is not improbable that these growths 

 assist in the progressive formation of invert-sugar which 

 frequently takes place during the storage of cane-sugar. 



Hansen has observed many different species, and has 

 described the following in detail : 



The first occurs in wort, the cells being either single or in 

 small clusters. Some cells have a large vacuole in the middle, 

 and this sometimes contains a small strongly - refractive 

 particle. The size of the cells varies considerably (1-5 to 

 4-5 /A). This species does not secrete invertase, and causes 

 a scarcely perceptible alcoholic fermentation in beer- wort. 



Under the same conditions the second species possesses 

 larger cells than the first (3 to 8 ju) ; they resemble the fore- 

 going, except that the contents of the cells grown in wort are 

 often very granular. 



The third species which, micro- 

 scopically, resembles the last, produces 

 under the same conditions as much as 

 0-88 per cent, by volume of alcohol ; 

 it gives a distinct head with evolu- 

 9^rnrfaoifter Hansen).- tion of carbon dioxide, but it cannot 



Sedimentary forms after one 



day's cultivation in beer-wort invert Cane-SUgar. 



The fourth species (2 to ^6 /z) inverts 



cane-sugar and produces slightly more than 1 per cent, by 

 volume of alcohol in wort with considerable frothing ; it does 

 not, however, ferment maltose. 



The fifth species, which in the form and size of its cells 

 resembles the first, develops a uniform, dull grey film on wort 

 and yeast-water at the ordinary room temperature, likewise 

 on lager beer, and even on liquids containing as much as 10 

 per cent, of alcohol. It inverts cane-sugar, and forms a slight 

 film on the solution. It does not, however, excite any appreci- 

 able alcoholic fermentation. 



A sixth species (Fig. 89), which forms spherical and oval 

 cells, gives a distinct fermentation in beer-wort, yielding as 

 much as 1-3 per cent, by volume of alcohol. It does not 

 ferment maltose solutions. It inverts cane-sugar, and in 

 10 per cent, and 15 per cent, solutions of this sugar in yeast- 



