CHAPTER XXV. 

 MOULDS AND YEASTS. 



MOULDS, yeasts, and other minute fungi are almost as 

 widely distributed as bacteria, and the student of 

 bacteriology is constantly meeting with them both as 

 impurities in his cultures, and upon butter, cheese, and 

 other materials with the study of which he may be 

 largely concerned. 



Some of these fungi are of great technical importance, 

 and there is no doubt that many of the yeasts and 

 moulds found in the soil, in manures, and in the interior 

 and on the outside of cheese and other dairy products 

 play considerable part in the characteristic chemical 

 changes which go on in these materials. 



The complicated chemical fermentations occurring in 

 the putrefaction and decay of manure and organic matter 

 in the soil, as well as in the " ripening " of cheese and 

 other foods, are often the result of the symbiotic or com- 

 bined activity of moulds, yeasts, and bacteria working 

 simultaneously. 



The present chapter deals with the chief morpho- 

 logical characters of the common kinds of moulds and 

 yeasts. 



Moulds. 



i. The genus Penicillium. One of the most frequently 

 encountered small fungi, is common blue mould (Penicillium 



glaucum, Brefeld). The body of the plant is composed of 

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