GENERAL BIOLOGY 



color of the cell due to the cell wall or contents? Is there any 

 opening in the sac through wh ich food can be ingested ? Are there 

 any organs of locomotion? Is the wall elastic? (b). What is the 

 physical nature of the contents ? Its color? 



Draw several cells to show size, mode of union and structure. 



B. CHEMICAL REACTION. 



1. Run a drop of aceto-carmine under the cover glass and ob- 

 serve which individuals stain soonest and most deeply. Do the 

 crushed cells stain as readily as the entire ones ? Does the sac stain? 



2. Treat another drop of yeast with dilute caustic potash. 

 What happens to the cells? 



3. Kill some yeast cells by boiling them with water in a test 

 tube. Mount some of this dead yeast and stain with aceto-carmine. 

 Does it stain differently from the living yeast? What inferences 

 may be drawn? 



4. Mount a fresh drop of yeast on a slide and treat with a drop 

 of iodine. What is the effect on the cells? Is starch present in the 

 fluid? Is there any starch in the cells themselves? 



Make drawings of the yeast cells showing the effect of the 

 reagents. 



C. PHYSIOLOGY. 



In the following experiments the amount of growth which has 

 taken place may be roughly measured by the increase of the tur- 

 bidity in the liquid. It may be tested microscopically by the num- 

 ber of buds to which the cell has given rise. 



i. Effect of food supply upon growth. Take five test tubes, 

 each one-third full of the solution named: (a) distilled water; 

 (b) 10 per cent solution of sugar in water; (c) Pasteur's solution 

 without sugar; (d) Pasteur's solution with sugar; 4 (e) Mayer's 

 pepsin solution. 5 



Carefully label each tube and put a drop of yeast into each; 

 shake the tubes thoroughly and tightly plug the mouth of each 

 with a wad of clean absorbent cotton and allow them to remain 



*Pasteur's Solution : 5 Mayer's Solution : 



Potassium phosphate 2.0 grams Cane sugar 15% sol. ...20 cc. 



Calcium .2 Dihydropotassic phos- 



Magnesium sulphate .2 phate I grams 



Ammonium tartrate 10.0 Calcic phosphate I 



(Cane sugar 150.0 " ) Magnesium sulphate ...I 



Distilled water 837.6 Pepsin 23 



[32] 



