286 PROPERTIES CONFERRED BY COLLOIDAL CONSTITUENTS 



the Lecithins, partly in a very finely emulsified form, the individual 

 particles being of ultramicroscopic dimensions, and partly in a 

 coarsely emulsified form such as that found in fatty connective tissues. 

 The presence of a large proportion of ultramicroscopically divided fat 

 is shown by the high fat-content of many tissues in which microscopical 

 examination after appropriate staining fails to reveal the presence of 

 visible fat-globules. Under certain conditions, especially in Phosphorus- 

 poisoning and in Anaphylactic Shock, the ultramicroscopic particles in 

 certain tissues coalesce to form coarse emulsions and the particular 

 tissues affected, as for example the liver in phosphorus-poisoning, are 

 then easily seen to be heavily infiltrated with fat. Direct analysis, 

 has shown that in such cases the fat-content of the tissues is neverthe- 

 less normal, in other words the normal liver-cell contains just as much 

 fat as the liver-cell which has undergone fatty degeneration in conse- 

 quence of phosphorus-poisoning, but in the normal cell the Emulsifica- 

 tion of the fat is so thorough that the greater part of the fat is present 

 in particles too small to be visible under the microscope. The soluble 

 lipoids and the soaps and other substances which reduce the tension of 

 an oil-water interface are probably in large proportion concentrated 

 at the extensive surfaces which arise from this subdivision. 



The Emulsification of fats in water is greatly facilitated by the 

 presence in the water of a substance which reduces the interfacial 

 tension, provided that at the same time the substance forms a viscous 

 or sparingly soluble coating over the oil-droplets which retards their 

 coalescence when they come fortuitously into contact with one another. 

 We have already had occasion to dwell upon the importance of soaps 

 and of the bile-salts in bringing about the emulsification of the fats in 

 the diet prior to their hydrolysis by the digestive enzymes. 



When olive oil is shaken up with pure water little or no emulsification 

 occurs. Even when the mixture has been very thoroughly shaken, 

 the oil and water separate completely within a comparatively brief 

 period. If, however, a little sodium carbonate or hydroxide be added 

 to the water in order to form soap with the trace of fatty acid which oil 

 contains, the effect of shaking the mixture is now very different. A 

 milky or creamy emulsion is formed with comparatively little expendi- 

 ture of mechanical effort in shaking, and no separation of the two 

 fluids will occur even after long intervals of time. The emulsifying 

 action of alkalies is also strikingly illustrated by floating drops of Olive 

 Oil upon distilled water and one per cent, sodium carbonate solution 

 respectively. In the latter case the oil-droplet spreads out, fluctuations 

 of superficial tension at the edges of the drop cause deformations, and 

 result in a species of "fraying" of the edges, minute particles of the oil 

 breaking off to form a milky emulsion which gradually spreads through 

 the solution. 



In the Emulsions of oil in water which are thus formed the spherical 

 droplets of oil are surrounded and completely enveloped by the water. 

 The power of a given quantity of water to surround oil must evidently 



