APPENDIX 303 



23. CO2 produced chemically. In test tube <z of a pair of tubes 

 similar to those used in the last experiment place a little cream of 

 tartar in water; in another test tube dissolve some saleratus in water. 

 Pour the saleratus solution into test tube a, close at once with a cork, 

 and allow the gas produced to pass into limewater as before. 



Microscopic Study of Yeasts 



24. Resting Stage. Rub a bit of yeast cake in a little water so 

 as to make a slightly cloudy solution. Place a drop of the solution 

 upon a microscope slide, cover with a cover glass, and examine first 

 with a |-inch objective. Note that the water seems to be filled with 

 very minute dots. Study with a higher power (^inch objective). 

 Examine the yeast cells, noting the shape, comparative size, and the 

 vacuoles inside of the cells, as shown in Fig. 32. Are the cells 

 attached or are they mostly separate? Hunt for small buds upon 

 the sides of the larger cells. Proceed in the same way with a little 

 dried yeast cake and compare the yeast cells in size and appearance 

 with those of compressed yeast. 



25. Growing Yeast. With a pipette remove a drop of the sedi- 

 ment from growing yeast prepared as in Experiment 21. Place 

 the drop on a slide, cover with a cover glass, and study as in the 

 previous case. Remove some of the yeast found floating on the sur- 

 face, and study in the same way. Note that the yeast cells are in 

 groups. Make a sketch of several groups, showing buds of various 

 sizes. Can you see the vacuoles in the cells, as in the first specimen ? 

 Note any other differences you can see between this growing yeast 

 and the compressed yeast cake. 



26. Staining Yeast. Place a drop of yeast upon a slide and cover 

 with a cover glass. Place a drop of stain upon the slide beside the 

 specimen. (Almost any stain will do. Eosin dissolved in water is 

 satisfactory.) With a bit of blotting paper applied to the edge of 

 the cover glass opposite to the stain, draw the water out so as to 

 suck the stain under the glass. Allow the stain to remain about two 

 minutes, and then place a drop of clear water beside the cover glass 

 and with a blotter draw this under until it washes out the stain. 

 Then examine the specimen and determine whether the yeast cells 



