A STUDY OF LIVING SUBSTANCE 



37 



Fermentation. And so we learn that yeast, as it grows in 

 the molasses mixture, changes the sweet substances into car- 

 bon dioxid and alcohol, a process that is known as alcoholic 

 fer-men-ta'tion. 



Microscopic Appearance of Yeast. While watching the 

 yeast experiments, we see on the bottom of the bottle a 

 dense, white sediment. If we examine with the microscope 

 a bit of this sediment, we find that it consists t>f innumerable 

 bodies of minute size. These are yeast cells. Each cell is 

 more or less egg-shaped, and is composed of colorless proto- 

 plasm inclosed within a wall of cellulose. By the use of 

 special stains, a nucleus becomes visible. (The spherical 

 dots seen in fresh yeast cells are known as " vacuoles " and 

 are filled with a color- 

 less liquid.) Yeast is 

 regarded as one of the 

 lowest forms of plant life. 

 Reproduction of Yeast. 

 Most of the cells that 

 we are looking at are 

 not separate individuals, 

 but are strung together 

 in little chains. This 

 fact leads us to a discus- 

 sion of the method of 

 reproduction of yeast. 

 When there is a suffi- 

 cient supply of food, 

 moisture, and Oxygen, Magnified about 200 times. Photographed 



through the microscope. One can see 

 single cells, mother-and-daughter colo- 

 nies, and near the center a mother cell, 

 two daughter cells, and a granddaughter 

 cell. 



Fia. 12. Yeast Cells. 



and when the tempera- 

 ture is favorable, these 

 living plant cells begin 

 to feed and to grow. 



They soon reach their full size, and then the cell wall is 

 pushed out at the side by the growing protoplasm. In 

 this way a bud is formed. This continues to grow and 



