216 MICRO-ORGANISMS AND FERMENTATION. 



with rounded corners (Fig. 42 : 3, 6, 17 to 19) ; in a growth of 

 this mould spherical, oval, pear-shaped conidia, and others of 

 quite irregular form are, however, almost always present 

 (Fig. 42: 4, 5, 11 to 14). These organs of propagation, the 

 only ones known, send out one or more germ tubes. When 

 the fungus grows on solid substrata, the hyphse unite and form 

 remarkable conical bodies. 



Fresenius correctly gave to this species the specific name 

 of lactis ; for universal experience shows that it has its ordinary 

 habitat in milk, where it can usually be found. It also occurs 

 spontaneously in various other liquids, and among these in 

 the saccharine liquors which are employed in the fermentation 

 industries : in the latter it is able to induce a feeble alcoholic 

 fermentation. Thus, according to Lang and Freudenreich, it 

 produces in milk and grape-sugar solutions, in the course of 

 about ten days, 0-55 per cent., and in five weeks, 1 per cent, by 

 volume of alcohol ; smaller proportions of alcohol are produced 

 in cane-sugar and maltose solutions. Its maximum tem- 

 perature is, according to Hansen, 37-5 C., and its minimum 

 below 0-5 C. Cultures made in lactose nutritive solution 

 develop a powerful odour, resembling that of soft cheese, 

 such as Limburg cheese. Oidium is thought by Weigmann, 

 Conn, and others to play some part in the ripening of Camem- 

 bert cheese. It is believed that Oidium is of importance in 

 the ripening of this and other kinds of cheese, because it 

 absorbs the acids produced by lactic acid bacteria, and thus 

 paves the way for peptonising bacteria. Casein, in sterilised 

 milk, is rapidly decomposed by the fungus. According to 

 O. Jensen, an Oidium is always present in rancid butter. 



The fungus may occur in beer, especially when poor in 

 alcohol. As the amount of alcohol increases, the conditions 

 for its growth become less favourable ; still, neither wort nor 

 beer is exposed to the danger of being attacked to any extent 

 by Oidium, since it is not able to compete in the struggle for 

 existence with the crowd of organisms which at once appear 

 when fermentable liquids are exposed to the atmospheric 

 germs. 



In numerous investigations with top-fermentation yeast, 

 the author has found that it offers a very favourable nutritive 



