32 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



18. Liesegang Rings. — Pour a little 8.5% silver nitrate on gelatin gel 

 in a test tube containing 0.1% potassium dichromate. Place in the ice- 

 box for a day or two. Observe the rhythmic banding. Explain (cf. 

 Scarth, and Lloyd, p. 161; Hedges and Myers, "The Problem of Physico- 

 chemical Periodicity," p. 21, 1926). Text p. 161. 



19. Epithelial Tissue. — Make a 10% solution of gelatin and pour in a 

 Petri dish. When it has set place uniform drops of 5 or 10% ferrocyanide 

 solution equally spaced at intervals of 5 mm. over the plate. Cover and 

 set aside until next day. Observe the tissue formation (cf. Ponder, 

 "Essentials of General Physiology," p. 108). Text p. 163- 



CONTRACTILE SYSTEMS 

 Vn. AMOEBOID MOVEMENT 



1. Normal Movements. — Observe an amoeba in motion. Note direc- 

 tion of protoplasmic streaming. Compare with physical models of amoe- 

 boid motion previously studied. Could amoeboid movement cause 

 cytoplasmic fission? (cf. SchaefFer, "Amoeboid Movement" 1920; 

 Chalkley, Protoplasma, 24: 607, 1935). Text p. 274. 



2. Influence of Substratum. — Place an amoeba in a weak gelatin solu- 

 tion to eliminate contact with substratum. Is movement impossible? 

 (cf. Haycroft and Carlier, Proc. Roy. Soc. B, 15: 220, 1888; also 

 D'Arcy Thompson, "Growth and Form," p. 211). 



3. Mechanical Stimulus. — ^Touch the amoeba with a fine glass point. 

 Note any change in direction of locomotion, in streaming, or contact with 

 substratum. The reaction is slow. Cf. Seifriz, "Protoplasm," p. 57- 



4. Chemical Stimulation. — Bring the tip of a fine capillary containing 

 various solutions against the side of an amoeba. Try NaCl, Sugar, HCI. 

 Note reaction, if any. Allow a drop of methyl violet to diffuse toward 

 an amoeba. Result? Cf. Jennings, "Behavior of the Lower Organisms," 

 p. 187, 1904. 



5. Electrical Stimulation. — Observe an amoeba when electric shocks 

 are sent through the water on a slide by means of 2 strips of tin foil (mak- 

 ing good contact with the water on each side), and connected to an induc- 

 torium (2 dry cells). Begin with very weak shocks and note the effect 

 on the protoplasm of the amoeba. Compare with the response of Trades- 

 cantia protoplasm described by Kiihne. Cf . Bayliss, pp. 21-22. Note the 

 form of minimal area. Text p. 76. 



6. Contraction of Plant Protoplasm. — Repeat the experiment using 

 filaments of Spirogyra placed lengthwise in water on a slide. Sketch a 

 cell showing spirals contracted by the protoplasmic threads (cf. Scarth 

 and Lloyd, p. 33). 



