THE FUNGI. 151 



6. Examine for the nucleus. Prepare a dry layer of 

 yeast on a cover glass ; fix the cell contents by allowing 

 the cover glass to remain in a strong solution of picric 

 acid for twenty-four hours. Wash thoroughly in water 

 to remove the picric acid, and stain in ammonia hoematoxy- 

 lin, which may be prepared by shaking some of the hyema- 

 toxylin crystals in distilled water to which a minute drop 

 of aqua ammonia has been added. Allow this stain to 

 act for several hours, but do not let it dry on the cover 

 glass. Wash thoroughly in water and mount. The 

 nucleus will now be seen in the center of the cells as a 

 small round mass more deeply stained than the rest of 

 the cell. 



7. Prepare two test tubes containing actively growing 

 yeast. Wrap one in opaque paper. Stand the two tubes 

 in the bright light of a window. Prepare two other 

 tubes in the same way and stand in the diffused light of 

 the back part of the room. Does the presence or absence 

 of light affect the growth of the yeast ? 



8. Grow yeast in Pasteur's solution in a flask, connect- 

 ing the flask by means of a delivery tube with a beaker of 

 clear lime water. After a time the lime water becomes 

 cloudy because of the formation of carbonate of lime 

 occasioned by the union of carbon dioxide, given off by 

 the growing yeast, with the lime water (calcium hydrox- 

 ide'). Distil what remains in the flask until about one 

 fifth of it passes over. Mix this distillate with potassium 

 carbonate and distil again. Observe a peculiar streaki- 

 ness on the neck of the retort ; this is characteristic of 

 alcohol. This distillate may further be proved to be 

 alcohol by its odor, by the fact that it will burn, and by 

 the green color and fruity odor produced when a little of 

 it is boiled after the addition of a few drops of a solution 

 of potassium bichromate and of sulphuric acid. A sub- 

 stance which has the power to effect decomposition as the 



