356 FUNGI 



beer they are the product sought, and every means is 

 taken to retain them. 



Before the action of bacteria and yeast were understood, 

 much trouble was experienced in getting uniform products, 

 owing to the presence of undesirable bacteria and yeasts. 

 The possibility of making pure cultures, the use of the 

 microscope, as well as the tests which are made in the 

 laboratories at every step of the manufacture, have placed 

 the industries of bread-making and brewing on a scientific 

 basis. 



251. Reproduction of the Yeast Plant. — The method of 

 reproduction of the yeast plant is similar to that of the 

 bacterium, but differs from it in that instead of dividing: 

 exactly in two, a bud usually pushes out from the side of 

 the mature plant. Sometimes the second plant will form 

 a bud before it breaks awa}^ from the first, and so a chain 

 is made. Oftentimes a single plant puts forth more than 

 one bud (Figure 374). 



LABORATORY STUDY 



Prepare a Pasteur solution, a good food for yeast, as follows : 



Potassium phosphate 10 parts 



Calcium phosphate 1 part 



Magnesium sulphate 50 parts 



Ammonium tartrate 50 parts 



Cane sugar 750 parts 



Sufficient water to make a total of 5000 parts. (This may be used for 

 the culture of other molds than yeast and also for bacteria.) 



Yeast. — Examine yeast cells under low power. Note their glistening 

 appearance and their number. Under the high power try to find all parts 

 of a typical cell. Label and draw. Look for budding cells and chains 

 of cells. Draw. Make a thick paste of water, yeast, and flour. Put an 

 equal amount into each of three tumblers. Place one tumbler in a cool 

 place. Into one of the remaining stir a teaspoonful of sugar and set both 

 tumblers in a warm place. Examine several times a day and write down 

 all the differences you observe in the three mixtures. Try to give a reason 

 for everything you observe. 



