DIGESTION AND ABSORPTION OF FATS. 445 
oleic acids), prepared from sheep r 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 sunn 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 acid-, the 
phenomenon Avas accompanied by a chemical decomposition ; for the bile, 
which Avas neutral or slightly alkaline before the experiment, had become 
strongly acid after being treated Avith the fatty acid. 
"An experiment was now instituted to determine Avhether a similar 
phenomenon takes place when bile and neutral fats are mixed together. 
Indeed, it Avas 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, haA T ing a neutral reaction ; on agitating the 
hot mixture the globules of fat Avere 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 
Avas probably the chief function of the hit -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 on 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 a\ hen 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 (\ per cent, sodium carbonate). 
The following- are the main conditions which influence the format inn 
O 
of spontaneous emulsions, according to Gad : — 
1. The poAver 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 Avith 
1 Kiihnc, ' : Physiol. Chem.," 1866, S. 129 ; Briicke, Sitzimgsb. </. k.Akad. d. U'isscnsch., 
Wien, 1870, Bd. lxi. Abth. 2, S. 362 ; J. Steiner, Arch./. Anat. u. Physiol., Leipzig, 1874, 
S. 286 ; J. Gad, ibid., 1878, S. 181 ; G. Quincke, Arch./, 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. 
