106 GENERAL BIOLOGY 



the effect of the different conditions upon the growth 

 of yeast, and upon its power to cause fermentation, 

 (c) Fermentation. Conduct some of the gas being formed 

 in a culture of vigorously growing yeast through lime- 

 water or baryta-water. What is the effect on the 

 lime-water? A milky appearance or a white pre- 

 cipitate indicates the presence of carbon dioxide. 

 Is this the gas which is being produced by the yeast? 

 Permit yeast to grow in a large flask of Pasteur's 

 solution until growth has ceased, i. e., until gas is no 

 longer evolved. Distill the contents of the flask at 

 a low temperature (about 80 C) and test the dis- 

 tillate for alcohol by odor, taste, and inflammability. 

 (The test will be more certain if a second distilla- 

 tion is made.) What conclusions can you draw from 

 the experiment? 



From the experiments upon the life and activities of 

 yeast write a report clearly showing the nature of the experi- 

 ments, the results, and the conclusions which may logically 

 be drawn from them. Give a summary of the conditions 

 which are favorable and those which are unfavorable for 

 growth and ferment action of yeast. 



