238 MICRO-ORGANISMS AND FERMENTATION. 



inverting enzyme. It is not improbable that these growths 

 assist in the progressive formation of invert-sugar which 

 frequently takes place during the warehousing 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 M). This 

 species does not secrete invertase, and causes a scarcely per- 

 ceptible alcoholic fermentation in beer-wort. 



The second species has, under the same conditions, larger 

 cells (3 to 8 /x) than the first ; they resemble the foregoing, 



FIG. 75. Torula : sedimentary forms after one day's cultivation in beer-wort at 25 C. 

 (After HANSEN.) 



except that the contents of the cells grown in wort are often 

 very granular. 



The third species which, under the microscope, 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 

 evolution of carbon dioxide, but it cannot invert cane-sugar. 



The fourth species (2 to 6 /m) inverts cane-sugar and pro- 

 duces a little 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 

 appreciable alcoholic fermentation. 



A sixth species (Fig. 75), which forms spherical and oval 



