26 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



9. Effect of Temperature upon Rate of Digestion. — Make up four 

 tubes of soluble starch solution (3 cc. stock starch solution + 3 cc. H2O in 

 each). Place tube 1 in cracked ice; 2, in water bath at 15°C.; 3, in water 

 bath at 30°C.; keep tube 4 at room temperature. Add 0.5 cc. of enzyme 

 preparation to each. Observe time intervals for digestion by the same 

 method as in the first exercise (cf. Gortner, "Outlines of Biochemistry," 

 p. 727, 1929). 



10. Effect of pH upon Rate of Digestion. — Place 3 cc. of stock starch 

 solution in each of 4 test tubes. Add 3 cc. of S0rensen's phosphate mix- 

 ture (pH = 5.288) to 1; 3 cc. mixture (pH = 6.239) to 2; 3 cc. mixture 

 (pH = 7.168) to 3; 3 cc. mixture (pH = 8.043) to 4; add 0.5 cc. of enzyme 

 solution to each; note digestion times. Then test the pH of each tube by 

 the spot plate method to get the pH of each total mixture (cf. Gortner, 

 p. 723, 1929). 



Demonstration: Specificity of Enzyme Action. — Fermentation tubes, 

 containing the same amount of yeast suspension but a different sugar in 

 each, show the remarkable specificity of enzymes. The sugars used are: 

 (1) glucose; (2) lactose; (3) galactose; (4) mannose; (5) xylose. Note how 

 these sugars vary structurally. For specificity of enzymes, cf. Gortner, 

 p. 528; Bayliss, p. 328; Mitchell, 2nd Ed., p. 492. 



VI. PLASMOGENY 

 (PHYSICAL AND CHEMICAL MODELS OF LIVING SYSTEMS) 



1. Mercury Amoeba. — Place a large drop of Hg in a watch glass of M/3 

 H2SO4. Place a crystal of K2Cr04 near the Hg and note amoeboid move- 

 ments and "feeding" (cf. Bernstein, Pfliiger's Arch., 80: 628, 1900). 

 The interfacial tension of Hg is 375 dynes/cm. while that of a living 

 amoeba is only 1-3 dynes/cm. (cf. Harvey and Marsland, Jl. Cell. Comp. 

 Physiol., 2: 75, 1932). Text p. 171. 



2. Ostwald's Physical Heart, — Place a large drop of Hg in a large 

 watch glass (10 cm. diameter) of 2% HNO3 (or 10% H2SO4). Clamp a 

 sewing needle (with femur clamp on stand) so that the point just touches 

 the Hg. Explain the rhythmic action due to the negatively charged 

 carbon in the needle. Note odor of C2H2. Cf. Burns, "Biophysics," 

 p. 49. To prevent cessation of pulsation by polarisation, a trace of K2Cr04 

 solution may be added (cf. Pohl, "Physical Principles of Electricity," 

 p. 278, 1930). Text p. 190. 



3. Mercury Octopus. — Place a large flat drop of Hg in a Petri dish of 

 40% H2SO4. Connect wires to a dry cell and draw out tentacles from the 

 Hg with the positive pole. Now touch the octopus with the negative 

 electrode. Explain movement (cf. Bums, Fig. 10). Text p. 190. 



4. Formation of Foraminifera Shells. — Introduce a drop of a mixture 

 of powdered glass and chloroform under water in a watch glass, or intro- 



