YEASTS IN THE AIR 105 



air upon gelatine or agar plates, or upon sterilised potatoes, 

 and grow on the first-named in the form of round colonies 

 raised into knobs of a drop-like appearance, which do not 

 liquefy the medium. 



Pink yeast is distinguished by the rose-pink colour of 

 the mass, and shows on gelatine-plates small round, rather 

 coarsely-granulated, rose-coloured colonies. In thrust cul- 

 tures there appears after eight days a coating with a dull 

 surface like a drop of wax, which slowly increases in cir- 

 cumference and shows raised edges, while a row of little 

 dots forms along the track of the thrust. The gelatine is 

 not liquefied. On agar there grows an irregular thin slimy 

 coating of a pink colour, and on potato a deposit of a beau- 

 tiful rose-red tint. 



Black yeast and white yeast only differ in the colour of 

 the coatings formed by them. 



Yeast grows at the temperature of an ordinary room. 

 When stained with aniline colours the cells shrivel some- 

 what, and do not show the fine figures seen if they are 

 examined in the unstained condition. They can easily be 

 distinguished from cocci by their remarkable size (1*5 ^ to 

 3 //, long, 2 yu, broad). 



Micrococcus radiatus. The Microcpccm radiatus, iso- 

 lated by Fliigge, forms small cocci in short chains or 

 clumps. On gelatine plates little yellowish-brown colonies 

 first appear, from which outgrowths push forth in a radial 

 direction, and in thrust-cultures rays are seen running out 

 horizontally from the centre of the track, so that it ac- 

 quires an almost feathery appearance. The gelatine is 

 slowly liquefied. Colonies of a yellowish colour form on 

 potatoes. 



Micrococcus versicolor. This micro-organism, which 

 was also found by Fliigge, is distinguished by the mother- 

 of-pearl gloss seen on its colonies. It forms minute 



