10 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



between the lights with the intensity in foot candles. Record the paths 

 at several distances between the lights. Cf. Crozier, J. Gen. Physiol., 

 8: 671, 1927. 



19. Tonic Immobility. (Animal hypnosis). — Place a newt dorsum 

 down on a flat surface and observe the induced state of immobility. Will 

 limbs remain in any position if moved? Observe breathing. Determine 

 the average duration of immobility. Record the temperature (cf. 

 Hoagland, J. Gen. Physiol., 11:715, 1928; Steiniger, Ergebnisse Biol., 13: 

 348, 1936). 



II. SURFACE TENSION 



For quantitative methods, see Dorsey, Bureau of Standards Scientific 

 Papers, No. 540, vol. 2, p. 563, 1926; Duclaux, Capillarite, 1934. Text 

 p. 50. 



1. Floating Needle. — Draw a needle between thumb and finger to 

 cover it with oil. Carefully drop needle on surface of water. Note 

 depression of water film and explain why needle floats. Now clean the 

 needle with Na2C03 solution and repeat. Explain result (cf. Descartes, 

 1638, Les Meteores, Oeuvres vol. v, p. 187; Adam, "Physics and Chemistry 

 of surfaces," 1930, p. 191). Text p. 49. 



2. Submerged Ring. — A weighted cork supports a large wire ring in 

 the air above water in a deep jar. Submerge the figure and note that its 

 rise is arrested when the ring reaches the surface. (Surface tension figures 



I can be obtained from the Central Scientific Co.) 



3. Van der Mensbrugghe's Experiment. — Dip a wire ring with an 

 attached small loop of thread into soap solution to form a film that holds 

 the loop of thread. Puncture the film inside the thread loop with a hot 

 wire. Explain result (cf. Bayliss, p. 48). 



4. Maxwell's Example of Surface Tension. — Secure a rectangular 

 wire frame of which one side can slide along the two adjacent sides Dip 

 in soap solution to secure film. Hold frame horizontally and slightly 

 approximate adjacent sides to allow slide wire to move freely. Explain 

 result (Scarth and Lloyd, "Gen. Physiol," p. 21). 



5. Minimal Area Configurations. — Dip a cubical wire frame into soap 

 solution. Try dipping several times in succession. Sketch geometrical 

 patterns formedw Explain. Best results are obtained with Plateau's 

 solution (cf. C. V. Boys, "Soap Bubbles," p. 170, 1931). 



6. Bubbles. — Compare the shape of (a) a soap bubble freely floating 

 in air; (b) the same compressed or pulled out (hanging from pipe); (c) 

 two equal sized bubbles resting on soap solution in contact with one 

 another; (d) unequal bubbles in contact. Place a small bubble in contact 

 with a large one in a Petri dish of soap solution. How does the internal 

 pressure vary with the size of the bubble? To show the law of constant 

 mean curvature draw out a bubble between two clay pipes (cf. Scarth and 



