98 A MANUAL OF BACTEEIOLOGY 



FowLEB. Introduction to Bacteriological and Enzyme Chemistry. New York 



and London, 1911. 

 Const. Bacteria, Yeasts, and Molds in the Home. Boston, 1909. 

 Pasteur. Studies on Fermentation. New York, 1879. 

 Hansen. Practical Studies on Fermentation. Transl. by Miller. London, 1896. 



Exercise 137. Morphology of Yeast (Saccharomyces) 



Yeast plants are unicellular organisms which reproduce prin- 

 cipally by budding. Under certain conditions — for example, 

 a sudden diminution in food supply — they produce endo- 

 genous spores, usually two to six in each cell. This condition 

 is supposed to ally the yeasts with the Ascomycetes, and the 

 sporangia are regarded as asci. 



1. Mix a piece of compressed yeast with water, mount a drop 

 of the mixture, and examine with both low and high powers. 



2. Note the shape of a single cell. Are all cells the same 

 shape ? What is the size of single cells ? Compare with other 

 organisms studied. 



3. Study the finer structure of the yeast cell. Note 



a. Color, homogeneity, and transparency. Mount some yeast 

 cells in Schultze's iodine solution. This solution turns normal 

 cellulose blue, fungus cellulose yellowish-brown. Of which is 

 the yeast cell composed ? 



h. The protoplasm, a semitransparent, granular substance fill- 

 ing more or less of the cell cavity. The protoplasm often con- 

 tains small oil drops, recognizable by their powers of refraction. 

 Are they equally abundant in all cells? 



c. Vacuoles, spherical cavities in the protoplasm filled with 

 cell sap. How many vacuoles in each cell? 



d. The nucleus, a small spherical body which can only be 

 distinguished by the use of special stains. 



Exercise 138. Reproduction of Yeast by Budding 



1. Mount a drop of yeast culture which has grown for twenty- 

 four hours in liquid wort medium or on wort agar. 



2. Note the presence of cells which have formed small out- 

 growths, or buds. Do cells ever form more than one bud ? Are 

 all buds of the same size ? 



