CYTOLOGY 



27 



small flask and a tube led from the closed flask into a solution of 

 Ca(OH) 2 the character of the gas will be revealed it is carbon 

 dioxide, CO 2 . ' 



The cane-sugar gives the Pasteur solution a sweet taste. Taste 

 an yeast mixture that has been in the incubator twenty-four hours. 

 It has lost its sweetness and gained the taste of alcohol and CO 2 . 

 The yeast plant consumes sugar and breaks it up to CO 2 and H 2 O. 

 The alcohol and CO 2 are waste products which the yeast throws 

 out because they are useless to it. 



FIG. 6 



Saccharomyces, or yeast plant: a, isolated yeast cells; b, c, gemmation; d, endogonidia or 

 ascosporae; e, budding of the endogonidia. 



3. Place 5 c.c. of the yeast mixture in a test-tube and insert the 

 tube in boiling water for a minute, or hold the tube over a Bunsen 

 burner until the mixture comes to a boil. What is the influence of 

 the heat upon the life of the yeast? Is there any evidence that the 

 yeast has been killed; if so, what? 



4. Place 5 c.c. of an active mixture in a test-tube and add alcohol 

 (95 per cent.) drop by drop until a change is noticed in the activity 

 of the yeast. Has the yeast been stimulated? If not, what has the 

 effect been? Account for the results. 



5. To another 5 c.c. of active yeast mixture add crystals of common 

 salt, stirring gently to cause solution, and note results. 



