DISTRIBUTION OF YEASTS 63 



WHERE YEASTS ARE FOUND 



From the facts just mentioned it will readily be under- 

 stood that yeasts have a wide distribution, even though 

 they do not grow luxuriantly except in sugar solutions. 

 The spores are excessively minute and are capable of 

 being thoroughly dried without injury, in which condition 

 they will remain alive for months. These spores are 

 easily blown by the winds and distributed far and wide. 

 Even the bodies of the yeast cells in their resting stage, 

 before they have produced spores, may be dried, and for 

 considerable time suffer no injury. These dry yeast cells 

 will keep for weeks and sometimes for months without 

 losing their power of growth. The commercial dried 

 yeast cake, which will be referred to presently, contains 

 not yeast spores but simply dried yeast cells. These are 

 still alive and remain for a long time capable of growing 

 if placed in proper conditions of food and moisture. Such 

 dried yeast cells are very light and easily distributed by 

 currents of air. In such dried form yeast is distributed 

 in dust by the winds, and may be found almost univer- 

 sally present over the surface of the earth, except in the 

 middle of oceans and deserts. Elsewhere the air, the 

 soil, and the water are practically sure to contain yeast 

 in greater or less abundance. 



Such yeast plants, or yeast spores, blowing around in the 

 air have sometimes been called wild yeast, a name quite 

 convenient for distinguishing plants which are indiscrimi- 

 nately scattered in the air from those which we cultivate in 

 great masses for purposes of brewing, bread making, etc. 



