66 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



color of cells under microscope (cf. Bayliss, p. 139). Remove filaments 

 to unstained tap water to observe color. Usually the cells are injured 

 showing increased permeability when dead. Text p. 367. 



4. Permeability of a Liquid Layer as a Function of Solubility. — Very 

 carefully place a layer of chloroform having iodine in solution beneath 

 distilled water in a flask. Above the water carefully place a layer of 

 ether. Let the flask stand undisturbed. Set up a similar experiment in 

 another flask but use 1% KI (in which I is more soluble) instead of dis- 

 tilled water. The solubility theory of permeability proposed by Liebig 

 in 1849 is discussed by Stiles, "Permeability," 1924, p. 46. 



5. Traube's Copper Ferrocyanide Membrane. — Mix equal volumes of 

 10% CUSO4 and 2M sugar solution. Introduce a drop of the mixture 

 beneath surface of 1% potassium ferrocyanide solution in a small beaker. 

 Allow to stand. Explain changes in form (cf. Bayliss, p. 112). Text 

 p. 179. 



6. Artificial Cells with Protein Membrane. — Shake five drops of 

 chloroform in a small quantity of distilled water. On standing do drop- 

 lets of chloroform reunite? Repeat using egg white solution and chloro- 

 form. Note difference in behavior of chloroform droplets. Pour into 

 flat dish and allow to evaporate. Do interfaces between chloroform and 

 egg white disappear? Shake 10% solution lecithin (in chloroform) with 

 egg white solution. Allow chloroform to evaporate and stain contents 

 of flat dish with neutral red; use weakest possible solution of neutral red 

 to obtain a delicate tint which will show action of alkali on the cells; 

 examine under microscope; draw. Lecithin absorbs water as chloroform 

 evaporates; each cell is a watery solution of lecithin surrounded by a 

 modified protein film. To a small portion of these cells add N/500 

 NH4OH, and N/500 NaOH. Note the time for color change (yellow) 

 in each case. Ammonia is lipoid soluble. Cf. Bayliss, p. 136; contrast 

 with living cells. Try the effect of saponin. Harvey (Science, vol. 36, 

 p. 564, 1912) devised these cells as plasmogenic models of sea urchin eggs. 

 For recent speculations concerning the nature of the plasma membrane 

 cf. Danielli, Jour. Cell. Comp. Physiol., 7: 393, 1936. Text p. 175. 



7. Changes in Permeability of Beet Cells. — Cut slices of beet and wash 

 in tap water to remove contents of injured cells. Place controls in tap 

 water. Place slices in (a) 0.31M (1.82%) NaCl which is isotonic with 

 the protoplasm, (b) 1% CaCl2; (c) chloroform water. Boil several slices 

 in tap water and test with Benedict's reagent after adding a drop of con- 

 centrated HCl. 



Benedict's Test for Sugar. — Heat to boiling about 5 cc. of Benedict's 

 reagent in a test tube with a glass fragment to prevent bumping. Add 

 about 8 drops of sugar solution and boil for two minutes. If more than 

 2 or 3 tenths per cent sugar is present, the solution will be filled with a 



