STRUCTURE OF YEASTS 



77 



What are Yeasts 



Yeast plants are always microscopic, no species being 

 large enough to be seen with the naked eye. When these 

 tiny plants are massed together, as in a yeast cake, the 

 mass may form a bulk large enough to be seen. We can 

 see a yeast cake, 

 but the individual 

 yeast plant is not 

 more than -^ of an 

 inch in diameter, 

 and this is far be- 

 low the power of 

 the unaided vision. 

 By the microscope 

 alone we learn that 

 the yelst mass is 

 made up of millions 

 of minute bodies, 

 each of which is an 

 individual yeast 

 plant. 



The yeast plants 

 are much simpler than the molds. If a bit of a yeast 

 cake be mixed with a little water and examined under 

 the microscope, there will be found what is shown in 

 Fig. 32. There will be seen large numbers of minute 

 oval bodies, sometimes very nearly spherical or sometimes 

 considerably longer than broad. They are quite color- 

 less and nearly transparent, as seen under the micro- 

 scope, but whitish when seen in bulk. They have a 



d e 



Fig. 32. Common yeast very highly magnified. 

 Figs, a and b show vacuoles ; c shows a nucleus 

 n inside of the yeast cell ; d shows a budding 

 cell with the nucleus dividing; e shows the cell 

 divided, the new cell containing a bit of the 

 old nucleus. 



