YEASTS AND MOULDS 333 



It consists of round or oval cells containing a clear fluid 

 and no granules. It is not used older than one week's 

 growth, after which time granules appear in the cells. 



When budding very rapidly, delicate mycelial threads 

 are formed. It forms ascospores at 25 C. in thirty hours, 

 and at 12 C. in ten days. In brewing, yeast is added to 

 the beer wort (cooled to 16 C.), and fermentation takes 

 place. A brownish-yellow scum forms on the surface, 

 bubbles of gas (CO 2 ) escape, forming a foam, and alcohol 

 is formed in the liquid. This is the " high " fermentation 

 with " top " yeast, and takes place in several days. 



In some breweries " low " or " bottom " yeast is used, 

 and the fermentation is conducted at 5 C. The yeast cells 

 sink to the bottom as they are formed, and the whole 

 process takes a much longer time (fourteen days). 



In baking, the yeast converts the starch into sugar, and 

 then the latter into CO 2 and alcohol. The gas breaks 

 up the glutin into thin-walled cells. The subsequent 

 " baking" or heating kills the ferment, and drives off the 

 CO 2 and alcohol. 



Wild yeasts are usually termed torulcc. They have 

 oval or spherical-shaped cells, do not produce ascospores, 

 and have only feeble fermentative powers. Some of them 

 have been found to produce a true mycelium. 



Torula rosea (Saccharomyces rosaceus) is a pink torula, 

 which, growing on gelatin, agar, etc., produces raised 

 masses with a polished pink surface, similar to a piece of 

 coral. Microscopically, it shows rounded or slightly oval 

 cells, 5 to 8 micra in diameter, and containing a delicate 

 yellow pigment, which in the mass gives the pink shade. 



Torula niger (Saccharomyces niger) grows on gelatin as a 

 black heaped-up mass, resembling a piece of black sealing- 

 wax. On potato and bread paste it forms a dull sooty 

 crust, and in milk a black crust. It is met with in the air. 



Pathogenic yeasts have been described in connection 

 with (i) Multiple abscesses in bones, lungs, spleen, and 

 kidney, and ending fatally (Busse) ; (2) An illness simula- 

 ting diphtheria (Klein and Gordon) ; (3) Subcutaneous 

 myxomatous tumours (CurtiS) ; (4) Middle-ear disease 

 (Maggiora and Gradenigo) ; (5) A lupus-like skin disease 



