414 ILLUSTRATIVE EXPERIMENTS 



the centre of the space between the electrodes, making contact with them 

 and covered with a f in. glass. After 10 minutes the microscope is focussed 

 on the central layer of liquid (particles not in contact with glass and free 

 to move) and a current of 4-5 volts (keep amperage low) passed between 

 the electrodes. Determine the sign of the electric charge on dialysed iron 

 sol, gold sol, night blue, alkali blue, etc. Fit an eyepiece micrometer and 

 with a stop-watch determine the velocity of the particles in cm. per volt 

 per sec. 



35. Model to Illustrate some Phases of Urine Formation. (Fischer and 

 MacLaughlin.) Prepare some cups of sodium stearate by pouring the hot 

 stearate solution (1/10 molar) into a mould consisting of one beaker (120 c.c.) 

 suspended within another similarly shaped (350 c.c.). A cup is supported 

 on a nitration disc in a filter funnel whose stem enters the mouth of a 

 graduated cylinder. Another cylinder (gas jar) or bottle inverted may be 

 used as a constant level device. Fill the cup and the gas jar with the 

 solution. Invert the full jar and suspend it vertically so that its mouth 

 just dips below the surface of the fluid in the cup. From time to lime 

 measure the fluid in the lower graduated cylinder, say every hour. 



Try the following solutions : (a) water (3-6 hrs.), (b) molar sodium 

 oleate (24 hrs.), (c) NaCl 1/8 m., 1/4 m., and 1/1 m. (3-6 hrs.), (d) 1/8 m. 

 CaCl 2 (1-4 hrs.), (e) 1/8 m. NH 4 C1 (7 hrs.). 



Note increased flow with (c) and (d) ; initial increase and final decrease 

 of flow with (e) and total inhibition with (b). Test, in each case, the per- 

 fusion fluid, the perfusate and the cup, with phenolphthalein. How do 

 you account for your results ? Test the perfusates for fatty acids. Why 

 does pure water dissolve out more of the acid than do the salt solutions ? 



36. Mimicry of Cell Structure (Herrera after Harting). A crystallising 

 dish 18 cm. in diameter is filled with colloidal silica. This may readily be 

 prepared by dissolving freshly precipitated gelatinous silica in a solution 

 of ammonia (density 26). Silica is added till all the ammonia has been 

 driven off and the colloid has a density of over 1-032 (i.e. 3-5 per cent, 

 solid silica). (A solution of sodium silicate of a density of 1-020 may be 

 used instead of colloidal silica.) At one edge of the crystallising dish place 

 10-20 mgrms. of recrystallised potassium bifluoride. At the diametrically 

 opposite side of the dish place 5 gms. pure powdered anhydrous calcium 

 chloride. Cover and keep at 20 C. for 24 hours. Various structures which 

 may be stained by any of the dyes used by histologists may be seen, e.g. 

 nucleated amoebae, cells undergoing division, nuclear spiremes, granular 

 and honeycomb structures, etc. 



The figures are due to the strains produced in the silicate by the simul- 

 taneous formation of a colloid, calcium silicate and a crystalloid, calcium 

 fluoride. Silica, coagulated by a crystalloid, gives rise to a semipermeable 

 membrane, which, if it forms a sac round a crystalloid, may set up endos- 

 mosis. Slow amoeboid movements may be shown by some of the com- 

 plexes lying near the point of insertion of the CaCl 2 . Add a trace of alcohol 

 over the CaCl 2 , and more rapid diffusion ensues. 



37. Emulsions. 1. Take four test tubes and place in each 10 c.c. of 

 olive oil. In addition add to (a) a few drops of oleic acid and a drop 

 of alcoholic NaOH ; to (b) some (soft) soap solution ; to (c) a few drops of 

 oleic acid and about the same quantity of cone. Ca(OH) 2 solution and 

 allow to stand. Which gives the best emulsions ? 



