32 



THE BIOLOGY OF THE CELL 



touching it against the -side of the tube, shake 

 the tubes thoroughly, tightly plug the mouth of 

 each with a wad of clean absorbent cotton, to 

 prevent the entrance of dust, and set them in 

 the water-bath, heated to 35° C, for two or three 

 days. Examine the tubes from time to time and 

 notice what is taking place. More accurate re- 

 sults may be obtained in the following manner : 

 Prepare five moist chambers, using a drop of 

 each of the culture fluids given above, mix one 

 drop of fluid yeast with about a thimbleful 

 of distilled water, then mix a drop of this 

 diluted yeast with the drop of culture fluid 

 in the moist chamber, and watch under the 

 microscope from day to day the development of 

 the yeast cells in each kind of fluid. In which 

 solution does the yeast grow best? In which 

 solutions are bubbles of gas formed ? Can you 

 detect any relationship between the number of 

 bubbles formed and the amount of growth? 

 What relationship is there between the compo- 

 sition of the various solutions and the amount of 

 growth which takes place in each? Is growth 

 accompanied by anything else than the increas- 

 ing turbidity of the solutions and the formation 

 of bubbles ? Do you find anything besides yeast 

 cells growing in these solutions ? If so, how do 

 you distinguish them from yeast and how do 

 you account for their presence ? In what condi- 

 tion must the food be in order that it may be 

 absorbed? Why does the cell absorb "food 

 solutions " ? Through what must the absorbed 

 substances pass in entering the cell ? 



Taste of the ten per cent, sugar solution after 



