DIGESTION AND ABSORPTION OF FA TS. 445 



oleic acids), prepared from sheep's fat, as soon as the latter had begun fusing it 

 disappeared, and. finally the whole of the fatty acid 'was dissolved \ on standing, 

 however, it was observed that a very few extremely minute globules of fat rose to 

 the surface. As soon as the mixture had been allowed to become colder than the 

 temperature of fusion of the fatty acids, it assumed a turbid appearance 

 throughout, which gradually increased, the fluid becoming white and milky, 

 slightly coloured by the bile ; finally, if the fat present was in sufficient 

 proportion, the whole mass was converted into a semifluid paste, possessed of 

 a light green colour, and adhering so strongly to the sides of the vessel that it 

 could be turned upside down without letting out its contents. 



" On diluting this remarkable emulsion with water, its consistency only 

 was altered, becoming thinner, but no decomposition occurred ; on heating 

 the diluted mass, the emulsion was dissolved ; it disappeared, but no globules 

 of fat could be seen floating on the surface beyond the few minute specks 

 previously mentioned. Besides this physical action of bile on fatty acids, the 

 phenomenon was accompanied by a chemical decomposition; for the bile, 

 which was neutral or slightly alkaline before the experiment, had become 

 strongly acid after being treated with the fatty acid. 



"An experiment was now instituted to determine whether a similar 

 phenomenon takes place when bile and neutral fats are mixed together. 

 Indeed, it was hitherto generally admitted that bile had no action on neutral 

 fats. The results of my observations confirm this view, for in no case could I 

 succeed in obtaining an emulsion and chemical decomposition, by heating bile 

 with pure sheep's fat or with oil, having a neutral reaction ; on agitating the 

 hot mixture the globules of fat were broken up, but on standing they rose to 

 the surface, the bile being unaltered in its appearance and reaction. Conse- 

 quently, bile exerts no action on neutral fats." 



Since these experiments of Marcet, many observers have busied 

 themselves with the nature and mode of formation of emulsions. 1 



Briicke found that the presence of a certain amount of free fatty acid 

 was sufficient to emulsify the remaining neutral fat, and stated that the 

 provision of a sufficient amount of free fatty acid to emulsify the rest 

 was probably the chief function of the fat-splitting property of the pan- 

 creatic juice. He obtained emulsion of fats containing fatty acids with 

 diluted egg albumin, with bile, and especially with solutions of sodium 

 carbonate and of borax. Gad discovered spontaneous emulsion, and 

 carried out exact experiments 011 the most favourable conditions for the 

 formation of emulsions. A spontaneous emulsion means the formation 

 of a permanent emulsion without any mechanical assistance by shaking ; 

 such as occurs when a drop of oil containing a sufficient percentage of 

 free fatty acid (5-7 per cent.) is placed on an alkaline solution of suit- 

 able strength (J per cent, sodium carbonate). 



The following are the main conditions which influence the formation 

 of spontaneous emulsions, according to Gad : 



1. The power of different fats to form emulsions by contact with the 

 same fluid depends (a) on the amount of free fatty acid in the fat, (b) on 

 the solubility of the soaps formed from these fatty acids, (c) on the 

 viscosity of the fat. 



2. The power of the same fat to form emulsions in contact with 



1 Kiihne, " Physiol. Chem.," 1866, S. 129 ; Briicke, Sitzungsb. d. k. Akad. d. Wisscnseh,., 

 Wien, 1870, Bd. Ixi. Abth. 2, S. 362 ; J. Steiner, Arch.f. Anat. u. Physiol., Leipzig, 1874, 

 S. 286 ; J. Gad, ibid., 1878, S. 181 ; G. Quincke, Arch.f. d. ges. Physiol., Bonn, 1879, Bd. 

 xix. S. 129 ; v. Frey, Arch.f. Anat. u. Physiol., Leipzig, 1881, S. 382 ; Rachford, Journ. 

 Physiol., Cambridge and London, 1891, vol. xii. p. 72. 



