YEASTS AND MOULDS 



53 



they have no smell, and do not liquefy gelatine. On a fatty 

 medium this mould produces the characteristic smell and taste of 

 Roquefort cheese. Among the many similar forms which are 

 known, only those can be employed which form a perfectly 

 colourless mycelium. If they colour the nutrient medium yellow 

 or brown, or their conidia become brown instead of green after a 

 short time, they will colour the Roquefort cheese brown. Accord- 

 ing to Staub, a mould of this kind, Penicillium casei, will produce 

 on the surface of cheese yellowish brown spots which gradually 

 become reddish brown, and coalesce so that the whole of the rind 

 becomes coloured. On Camembert and other French soft cheeses, 

 are generally found Penicillium camembertii, which forms pale 

 green or greyish green conidia, and Penicillium candidum, which 

 forms conidia up to half a centimetre long, being perfectly 

 white even in the ripe state. Both these moulds liquefy gelatine 

 slowly. While all the species mentioned above form conidia 

 which are perfectly smooth and spherical when ripe, Penicillium 

 brevicaule forms irregular warty conidia (Fig. 51) ; this mould is 

 usually yellow or brown and grows on manure ; according to 

 Weigmann and Wolff, it produces a smell of turnips or onions in 

 milk and dairy products 1 . According to -Thorn, varieties of this 

 mould are often found on Camembert cheese. 



1 " Centralblatt f. Bakt.," 2 Abt., 1909, Bd. XXIL, p. 657. 



