302 Dr. G. Quincke on the Formation of Emulsions, 



litated by the bile. It is, on this account, as a physiological 

 question that the development and durability of emulsions has 

 more especially been studied. 



W. Kiihne (Physiologische Chemie,]). 129, 1866) and Brticke 

 (Wien. Sitzber. 1870, lxi. 2nd part, p. 363) were among the 

 first to demonstrate the influence of the soaps developed in 

 the small intestine on the formation of emulsions. The latter 

 showed that rancid oil, containing free fatty acid, when 

 agitated with dilute solution of the alkaline carbonates, 

 produces a perfect emulsion with much greater rapidity 

 than a neutral oil. He pointed out at the same time the 

 important part played in the process of digestion by the 

 free fatty acids, which, according to the discovery of Claude 

 Bernard, are separated in the intestinal canal from the 

 neutral fat by means of the pancreatic juice. More recently 

 Johannes Gad* made the interesting observation that small 

 quantities of oil, which contain free fatty acids, will form per- 

 fect emulsions by mere contact with alkaline solutions without 

 the aid of external or mechanical means, such as agitating or 

 stirring. This can be well shown by dropping a little cod- 

 liver oil into a *25-per-cent. solution of soda. 



From further investigation it appeared that the emulsifying 

 power depends on the viscosity and acidity of the oil, on the 

 concentration of the soda solution, and on the solubility in the 

 surrounding fluid of the soap formed from the fatty acid. By 

 adding common salt and bile to the alkaline liquid, this ten- 

 dency to dissolve is so far corrected that the facilities for the 

 production of a good emulsion are much increased. With 

 castor-oil, which is more viscous than other oils, the formation 

 of an emulsion was not observed. When the conditions for the 

 emulsion-formation were present, the surface of the drop of oil 

 threw off at once a milky substance into the surrounding liquid; 

 the drop formed protuberances at the side, and exhibited 

 alterations in form and movements which possess remark- 

 able similarity to those of the Amoeba. Smaller oil-globules 

 then split off; and these partly gave rise to the further pro- 

 duction of emulsion. Under the microscope with a low power 

 the vicinity of the drop was seen to be the scene of brisk action ; 

 the particles producing turbidity in the fluid were observed to 

 fly off in rapid gyrations from the surface of the drop, some- 

 times returning to it again. The remainder of the oil could 

 not by mechanical means be converted into emulsion in the 

 same liquid. 



Gad recognizes therefore, quite correctly, the conditions 



* Du Bois-Reymond's Arcliw filr Anatomie unci Physiologie, 1878. 

 pp. 181-205. 



