BACTERIA. 89 



of sugar, in which they form large slimy masses ("frog-spawn") 

 and multiply vigorously. The fungus forms chains of cocci, 

 two of which are always more closely united ; unlike earlier 

 observers, ZOPF found that these cocci present no differences 

 with reference either to their morphology or physiology ; spore 

 formation could in no case be proved. Consequently, the 

 analogy which was formerly assumed to exist between this 

 fungus and the algal genus Nostoc (implied in the name 

 Leuconostoc) falls through. 



Under certain conditions the cells are surrounded by a 

 strong gelatinous envelope, which consists of a mucilaginous 

 carbohydrate, the so-called dextran. This formation a pro- 

 duct of assimilation only occurs in the presence of cane and 

 grape -sugar, and riot in solutions of milk-sugar, maltose and 

 dextrin, because these carbohydrates cannot be assimilated: 

 the same applies to glycerine. In presence of the last-named 

 substances, or in potato-cultures, the species develops quite a 

 different form, in which the gelatinous envelope is completely 

 absent. 



The Leuconostoc ferments grape-sugar, cane-sugar (after 

 previous inversion), milk-sugar, maltose, and dextrin, with 

 production of gas and acid. The acid was shown to be lactic 

 acid. The fungus secretes an enzyme which inverts cane-sugar; 

 but no other enzyme could be detected. 



Especially characteristic of this fungus is its power of resist- 

 ing high temperatures, the younger growths possessing this 

 power in a higher degree than older cultures. Thus a growth 

 will stand gradual heating to 86-87 C. effected in the 

 course of some minutes. The most favourable temperature for 

 development lies between 30 and 37 C. 



It is also remarkable that the growth and fermentative 

 action of the fungus are very favourably affected by the presence 

 of considerable quantities of calcium chloride. 



Finally, a Streptococcus may be mentioned, which in the 

 manufacture of Edam cheese is deliberately added to the milk, 

 to make the latter ropy. This cheese gets its peculiar char- 

 acter from this treatment. 



