PROTOZOA. 143 



decay in water. This infusion should be examined every day. 

 If the bacteria become too abundant some of the surface water 

 may be poured off and fresh water added. The paramecia, 

 which are just visible to the naked eye, appear as a whitish 

 cloud in the water or may accumulate as a film at the surface. 

 Often a sufficient number for study may be secured by scraping 

 with a scalpel the matter which accumulates on the sides of the 

 vessel just beneath the water surface, even when they are not 

 sufficiently numerous to cloud the infusion. The cover-glass 

 should be supported by sediment or by bits of cover-glass. 

 Make outline sketches of everything which can be thus shown. 

 I. With the low power of the microscope study the follow- 

 ing points: 



1. Activities. Describe, and figure as well as possible, the 

 nature of all the movements of which the animal seems capable, 

 using arrows to indicate directions. Can you distinguish an 

 anterior from a posterior end? By what characteristics? 



Do you find any reasons for believing that the Paramecia 

 are sensitive to external influences? What evidences? To 

 what sorts of influences do they respond? Do they avoid ob- 

 jects? Do they collide with each other in motion? Do they 

 tend to collect? Where? Are they as active at the end of the 

 hour as at the beginning? 



Make a new preparation in which the Paramecia are uni- 

 formly distributed in a drop of water. Place a small grain of 

 salt at the edge of the drop. What is the result ? Watch the 

 individuals under the microscope as they come into the salt 

 solution. On a new preparation, try similarly a minute amount 

 of acetic acid (^ to y* per cent, solution) applied with a 

 capillary tube. Compare results. Try sugar, quinine. 



Do you discover any instances of division or conjugation? 

 If so, describe. 



2. General form of the body. How would you describe 

 its shape? To what degree is it capable of change? Is the body 

 symmetrical? Give evidences. Make diagrams showing your 

 idea of a cross-section through the middle; also of one, one- 

 third way from each end. 



