YEASTS AND MOULDS. 155 



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presence of pure air which is supplied through pipes leading into the vat. 

 The white scum or foam which forms is poured on fine sieves, washed 

 with sterile water, and then centrifugalized to remove most of the water. 

 This partially dry material is then pressed into cakes, thoroughly dried at 

 a low temperature, and wrapped in lead foil to exclude air. Starch is some- 

 times added as a dryer, but this is no longer necessary because of the improved 

 methods of manufacture. Good yeast should be of a yellowish color, easily 

 powdered and should have a pleasant "yeasty" odor. 



The so-called Chinese yeast, concerned in various fermentation processes 

 is a mixture of Mucor species, yeasts and bacteria. The following species 

 of mucor are prevalent M. racemosus, M. alternans, M. spinosus, M. 

 circinelloides and M . boidinii. These have the power of converting starch 

 into saccharine compounds, which are then acted upon by the Saccharomyces. 

 Various alcoholic ferments have been employed in China and Japan since 

 time immemorial. 



Nuclein is prepared from yeast and other vegetable cells and is very 

 much used in the treatment of certain diseases due to pathogenic bacteria. 

 It is said to have strong bacteriolytic properties and to increase phagocytosis. 



