30 PRACTICAL PHYSIOLOGY. [iV. 



ethereal solution fall on paper, e.g., a cigarette paper = a greasy 

 stain on the paper, which does not disappear with strong heat. 



(d.) To olive oil or suet add caustic potash, and boil. Stearin is 

 present in the suet and is glycerin-stearate, while olein in olive 

 oil is glycerin-oleate. When stearin is boiled with a caustic 

 alkali, e.g., potash, a potassic stearate or soap is formed, and 

 glycerin is set free. This is the process of saponification. 



Tri-Stearin. Potash. Potassic Stearate (Soap). Glycerin. 



(e.) Heat lard and caustic soda solution in a capsule to form a soa^; decom- 

 pose the latter by heating it with dilute sulphuric acid, and observe the 

 liberated fatty acids floating on the top. 



(/.) Proceed as in (<t.), and add to the soap solution crystals of sodium 

 chloride until the soaps separate. 



(g.) Shake oil containing a fatty acid, e.g., De Jongh's cod-liver 

 oil, with a few drops of a dilute solution of sodic carbonate. The 

 whole mass becomes white = emulsion. Examine it microscopi- 

 cally, and compare it with milk, which is a typical emulsion. 



In an emulsion the particles of the oil are broken up into 

 innumerable finer particles, which remain discrete, i.e., do not run 

 together again. 



(h.) Shake up olive oil with a solution of albumin in a test- 

 tube = an emulsion. Examine it microscopically. 



(/.) Gad's Emulsion Experiment. Place in a watch-glass a solution of 

 sodic carbonate (.25 per cent.), and on the latter place a drop of rancid oil. 



The drop comes to rest, but soon the oil 

 drop shows a white rim, and at the same 

 time a white milky opacity extends over 

 the soda solution. With the microscope, 

 note the lively movement in the neighbour- 

 hood of the fat-droplet, due to the separa- 

 tion of excessively minute particles of oil. 

 The white fluid is a fine and uniform 

 emulsion (fig. 15). This experiment has 

 an important bearing on the formation of 

 an emulsion in the intestine in connection 

 with the pancreatic digestion of fats. 



(/.) Eanvier's Emulsion Experiment. 

 Ranvier has shown that if a drop of lymph 

 taken from the peritoneal cavity of a frog 

 be mixed on a microscopical slide with a 

 FIG. 15. Gad's Experiment. drop of olive oil, on examining with a 



microscope where the two fluids come into 



contact, one sees emulsification going on before one's eyes, with the forma- 

 tion of fine particles of oil like the molecular basis of chyle (Comptes re.ndus, 



