YEAST 105 



in form, number and size of cells in a group. Explain the 

 differences. 



The chief method of reproduction in yeast is by asexual 

 budding or gemmation. How does this method differ from 

 fission in protozoa? 



2. Growth. In the following experiments the amount 

 and rate of growth may be roughly estimated by the in- 

 crease in the turbidity of the liquids; fermentation may be 

 indicated by the rate and the amount of gas produced. 



(a) Food Supply and Growth. Fill four test tubes (if 

 fermentation tubes are at hand better results will be 

 obtained by their use) half full of the following fluids, 

 and into each place the same amount of yeast from 

 the same culture. Keep all the tubes under the same 

 conditions. 

 (I) Distilled water. 

 II) 10 per cent sugar solution. 



(III) Pasteur's solution without sugar. 



(IV) Pasteur's solution with sugar. 



After several hours or a day observe the tubes and deter- 

 mine in which the growth and fermentation have been most 

 rapid and greatest. 



(6) Other Conditions and Growth. Prepare several tubes 

 with Pasteur's solution containing sugar, and to each 

 add the same amount of yeast. Place some of the 

 tubes in a warm place (about 35 C) ; some in a cold 

 place (on ice if possible) ; boil some and place with 

 the first ones; to some add a few drops of a poison like 

 mercuric chloride or formalin; place some tubes in 

 the sunlight and others in darkness. Into a similar 

 tube place some yeast filtrate. After several hours, 

 or on the next day observe the tubes and note all the 

 differences. Draw what conclusions you can as to 



