70 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



13. Rate of Diffusion of NH4OH and NaOH. — Cover one end of each 

 of two tubes with a collodion film tied tightly over the ends of the tubes. 

 Paste a strip of mm. paper on each tube. Fill the tubes with 2% agar- 

 agar colored by neutral red. Immerse the covered end of one tube in 

 N/100 NH4OH and of the other in N/100 NaOH. Measure the rate of 

 diffusion. Is there any real difference? Compare results with Exps. 

 8, 10, and 11. Plot the curve for the distance of penetration as related to 

 time. Text p. 2. 



14. Paradoxical Penetration of CO2 through Epidermis. — Make an 

 "artificial cell" by stretching frog's skin over the end of a glass tube, 

 holding it in place with a rubber band. Put in the tube an aqueous solu- 

 tion of phenol red made very slightly alkaline with NaHCOa. Suspend 

 the tube with the skin just below surface of N/100 H2SO4 colored yellow 

 with a drop of phenol red. Allow to stand 5 minutes. No change should 

 occur. Now with N/2 NaHCOs make the outside solution distinctly 

 alkaline. The internal solution soon becomes acid. Why? 



Prepare 3 such cells, with the skins inside out. Place in each 1 cc. of 

 phenol red solution at pH 7.4. Dip the first into N/10 HCl -f- NaOH to 

 pH 7.4, the second to HCl — > pH 7.4 with NH4OH, the third into 

 N/10 NaHCOs + CO2 at pH 7.4. Color external solutions with phenol 

 red. Stir contents gently from time to time. Observe for half an hour 

 (cf. Mitchell, 2nd Ed., p. 454, for discussion of permeability to CO2; 

 Gellhom, "Das Permeabilitatsproblem," p. 233, 1929; Jacobs, Am. J. 

 Physiol., 53: 457, 1920). Text p. 259. 



15. Perfusion of Kidney. — These experiments take time and skill; 

 several attempts are required to develop technique. Use bull frogs if 

 possible. 



(a) Is the Kidney Permeable to Large Colloidal Particles? — ^Prepare 

 fine cannula by drawing out medicine dropper in flame. Attach to small 

 burette with gum rubber tubing. Etherize frog. Fold back flap of skin 

 on belly (which will be sewed in place later) to expose fascia and muscles. 

 Observe abdominal vein in median line. Pass 2 ligatures under vein, 

 about }''2 cm. apart. Tie off" lower ligature. Cut halfway through vein 

 and insert cannula pointing towards head. Tie second ligature. The 

 burette should contain 5% azoblau. Fluid must flow from the cannula 

 slowly as inserted to insure absence of air bubbles. Allow 1-2 cc. of 

 fluid to enter very slowly over period of 10 min. Remove cannula, 

 tying second ligature tightly. Sew up flap of skin. 



After frog has recovered, in from 1-6 hours, catheterize to obtain urine 

 (insert steeply tapering curved glass tube into cloaca, withdraw and look 

 for blue color). Examine the excised kidney microscopically. 



(b) Concentration of Phenal Red in Urine. — Two aspirator bottles 

 are required each connected with gum rubber tubing leading to a fine 

 cannula. Bottle A containing oxygenated Ringer should be about 24 cm. 



