PHYSICAL CHEMISTRY OF CELLS 265 



ence in this regard between large and small drops? Wet the glass 

 rod with NaOH and repeat the experiment. (6) Drop a small 

 amount of paraffin oil in 70% alcohol. Increase the surface of 

 the oil by pulling out projections with a glass rod. Results? 

 Explain. (7) Float a clean rubber band on surface of clean water. 

 Touch water inside the band with rod moistened with olive oil. 

 Result? Touch the water outside band. Explanation. (8) Place 

 a crystal of camphor on water. Trace the direction of the move- 

 / ments. Touch the surface with a glass rod moistened in oil. Does 

 y this action bear any resemblance to living phenomena? (9) Place 

 a drop of Hg. in a watch glass. Note the form and size. Cover it 

 ,with 2% HNO 3 and place a crystal of K 2 Cr 2 O 7 1 cm. away from 

 it. Draw changes in shape of Hg. Compare with the behaviour 

 ^D of amoeba. (10) Prepare a cell as follows: with balsam fasten 

 * small glass rods to a slide at such a distance from each other that 

 they will support a cover glass. When dry, fill the cell with a 



Xjbmi 



ixture of 2 parts glycerine to one of 70% alcohol. Place on the 

 >ver glass. Introduce under the glass with a capillary tube one 

 Js small drop of clove oil. Result? (The drop should behave like 

 an amoeba). Now touch the cover glass with a hot wire or glass 

 rod. Result? (11) Into a drop of chloroform on a slide, introduce 

 the end of a small glass rod (1 cm. long). Result? Repeat, using 

 rods dipped in shellac, paraffin, gum arabic, NaCl, sugar. Does 

 this resemble "choice" of food in amoeba? Can you get the drop 

 of CHC1 3 seemingly to "ingest" "digest" and "excrete"? (12) 

 Artificial amoeba. Wet a piece of cardboard in one spot, 1 cm. in 

 diameter, with water. Cover this cardboard with olive oil, letting 

 the oil soak into the paper everywhere except, of course, at the 

 wet spot. Remove the surplus of oil and lay the cardboard flat 

 on the table. Place a drop of glycerine mixed with soot on the 

 cardboard at the edge of the spot where the water was. Study 

 the movements and draw. Can you satisfactorily explain pseudo- 

 podial movement as due entirely to surface tension effects? 



Colloids. 



(1) Effect of electrolytes on the swelling of gelatin. Soak a 

 sheet of gelatin in water. With a cork borer cut out discs of known 

 size and place them in a series of concentrations of acids, bases, 



