386 ELEMENTARY BIOLOGY. [CHAP. 



S. [Sow a few yeast-cells in Pasteur's solution in a moist 

 chamber and keep them under observation from day to 

 day ; watch their growth and multiplication.] 



9. [Spore-formation : take some dry German yeast ; sus- 

 pend it in water and shake so as to wash it. Let the 

 mixture stand for half-an-hour : pour off the super- 

 natant fluid, and, with a camel's hair pencil, spread out 

 the creamy deposit in a thin layer on fresh cut potato 

 slices or on a plate of plaster of Paris, and place with 

 wet blotting-paper under a bell-jar: examine from day 

 to day with a very high power (800 diam.) for spores^ 

 which will probably be found on the eighth or ninth 

 day.] 



B. Physiologv. 



(Conditions and results of the vital activity of Torula) 

 I. Sow a fair-sized drop of yeast in — 

 a. Distilled water. 

 Ik 10 per cent, solution of sugar in water. 



c. Pasteur's fluid without the sugar. 



d. Pasteur's fluid with sugar. 

 \e. Mayer's pepsin solution ^] 



Keep all at about 35" C, and compare the growth of the 

 yeast, as measured by the increase of the turbidity of the 

 fluid, in each case. "<:z" will hardly grow at all, "/J'" better, 

 *V" better still, '^/" well, and "^" best of all. Note that 

 bubbles of gas are plentifully evolved from both the so- 

 lutions which contain sugar. 



^ Mayer's solution (with pepsin) = 



15 per cent, solution of sugar-candy 10 cc. 



Dihydropotassic phosphate o* i grm. 



Calcic phosphate c i grm. 



"Magnesic sulphate o' i grm. 



Pepsin c 2 3 grm. 



