YEASTS 



25 



from 0.006 to 0.010 mm. in length (Fig. 9). The wall is very thin 

 and encloses a ramifying protoplasm with a single nucleus and numer- 

 ous vacuoles. The vacuoles vary in number and the nucleus, in some 

 cases, is of considerable size, being one-third of the diameter of the cell. 

 As the yeast cell grows one end may enlarge, gradually becoming the 

 size of the original cell. Yeast in this condition is said to be budding. 

 A short chain of cells may be formed in this way, the individuals sep- 

 arating and forming new organisms. Yeast not only multiplies in 

 this manner but also by the production of endospores which are 

 usually formed when the necessary nutriment is lacking. Certain 





Fia. 9. Yeast cells in compressed yeast and brewer's yeast. A, budding 

 cells; P, protoplasm; G, granules showing molecular motion; M, foreign 

 mold; B, bacteria; S, Cassava starch grains in yeast cake. Drawing by 

 Hogstad. 



substances have been found to be essential for the growth of yeast; 

 these include sugar, albuminous material or ammoniacal salts, sul- 

 phate of magnesia and potassium phosphate. For the study of 

 yeasts in the laboratory they may be grown in Pasteur's Solution, 

 consisting of potassium phosphate, 2 gm. ; calcium phosphate 0.2 gm. ; 

 magnesium sulphate 0.2 gm.; ammonium tartrate 10 gm.; cane 

 sugar 150 gm.; water sufficient to mr.ke 1000 c.c 



