PRINCIPAL GROUPS OF PLANTS. 49 



of sugar whereby alcohol is formed, was for a long time supposed 

 to be due to the presence of the living yeast cell or to the action 

 of living yeast protoplasm, and hence fermentation brought about 

 by living organisms was distinguished from those fermentative 

 processes where distinct principles such as diastase were involved ; 

 the former being known as " organized " ferments, while the 

 latter were referred to as " unorganized " ferments. Biichner 

 obtained from freshly expressed yeast a nitrogenous substance 

 capable of changing solutions of cane sugar or glucose into alcohol 

 and carbon dioxide. This principle he termed zymase, and it 

 has all of the properties of an enzyme or ferment and behaves 

 exactly as the living yeast cell in a sugar solution. In the living 

 yeast plant zymase is continually being formed and decomposes the 

 sugar which has diffused into the cell. 



Yeasts are used in the treatment of certain skin diseases, their 

 action being attributed to a fatty substance, ceridine. Other 

 principles found in yeasts as well as extracts are used in the 

 treatment of cancer. 



Under the name of Xerase a mixture is marketed consisting 

 of 150 parts of dried beer yeast, 20 parts of dextrose, 125 parts 

 of white clay or aluminum silicate, and 3 parts of a mixture of 

 nutritive salts. It is used in the treatment of putrid wounds, 

 ulcers, etc. 



The ginger beer plant, which is used in England for making a 

 beverage known as ginger beer, consists of a yeast {Saccliaro- 

 myces pyriformis) and a bacteria (Bacterium venniforme). 

 These two organisms live in a somewhat symbiotic relationship, the 

 yeast changing the sugar into alcohol and the bacteria developing 

 lactic acid (see Technical Mycology, by Lafar). 



Green and Yellow Mildews. — To the Ascomycetes also be- 

 long the green and yellow Mildews, Penicillium and Aspergillus, 

 so common in the household, the dairy, and the granary. These 

 plants produce profusely branching mycelia which form patches 

 upon or just under the surface of the materials upon which they 

 grow. These areas become soft and spongy and are always white 

 at first. After a time hyphal branches, which are more or less 

 flask-shaped, rise above the substratum, and by a process of 

 division at the end of the branch, or conidiophore, a spore called 

 4 



