After a careful study of amoeba, compare with what you find in 

 the two kinds of movement described below. 



163. The movements of some species of amoeba may be imitated 

 by causing a drop of water or glycerine to adhere to the substratum 

 more strongly on one side than the other. This can be done a- fol- 

 lows: Place a piece of smooth cardboard in the bottom of a flat 

 dish, and on a certain spot on the paper place a drop of water. Then 

 cover the whole with oil, which soaks into the paper everywhere 

 except in the spot covered by the drop of water. After it is well 

 soaked remove the drop of water and oil and proceed with the 

 experiments. Mix some soot with a drop of water, or better, glycer- 

 ine, and place this on the surface of the cardboard near the spot 

 that was protected. Allow one side of the drop to come against the 

 protected spot. What happens? How does the movement resemble 

 that of amoeba and how does it differ? Study the movement of 

 particles on the surface of such a drop. Lycopodium powder 

 sprinkled on the drop will make clear the surface movements. 



Or does amoeba move in the manner of the drop indicated below? 



164. Make a mixture of equal parts glycerine and water, add 

 some bone-black, and place two cr three drops on a clean mercury 

 surface. Mercury is not wet by the mixture. Powder lightly the sur- 

 face of the drop with lycopodium. Now place a very small drop 

 of 95 c /'t alcohol at one side of the glycerine drop. \Yhich way does 

 the drop as a whole move? Make a diagram of the currents within 

 (as shown by the lamp-black) and the currents on the surface (as 

 shown by the lycopodium ). Do they agree with those observed 

 in amoeba ? 



165. Perform exactly the same experiment but use a clean 

 glass surface instead of mercury. The glass surface is wet by the 

 glycerine water mixture. Do the results obtained here agree with 

 those observed in amoeba ? 



What are your conclusions in regard to the cause of movement 

 in amoeba ? 



D. COLLOIDAL SOLUTIONS 



In colloidal solutions the particles of solute are large and consist 

 of many molecules (distinction from solutions of crystalloids, e.g., 

 sugar). Hence these solutions resemble suspensions in many of their 

 properties. Usually the colloidal particles are electrically charged. 

 The charge keeps the particles permanently suspended by preventing 

 their union to form larger particles ; it also determines many of 



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