36 COLLOIDS IN BIOLOGY AND MEDICINE 



mation of surface skins, see page 346. Where oil globules occur in 

 aqueous solutions containing colloids, it may be assumed that they 

 are surrounded by a film of colloid which prevents them from run- 

 ning together and forming larger drops of fat. This is exemplified in 

 the emulsion of fats in the intestine and in the milky turbidity of the 

 serum after ingestion of fat as well as in the oleaginous and resinous 

 emulsions in plants, e.g., in the milky sap of the Euphorbiace. 



As has been already stated the same conditions obtain for the 

 interfaces between fluid/solid as for fluid/fluid. H. BECHHOLD ** 

 explains the action of protective colloids (see p. 11) as a mani- 

 festation of this phenomenon. Protective colloids form colloidal 

 films about the substance in suspension and thus impede the 

 coalescence (flocculation) of the separate particles. Consequently 

 surface pellicles afford stability to the metal sols, and permit their 

 practical utilization. 



On the other hand, suspensions and hydrophobe colloids, depend- 

 ing on circumstances and the surface tension, may either pass from 

 one fluid into another fluid with which it is not miscible, or they may 

 concentrate at the interface (REINDERS). This must be considered 

 in all studies on the distribution of colloids in the body, as in staining 

 with colloidal dyes and the injection of colloidal metals and possibly 

 even infection with micro-organisms. 



[According to the views of MARTIN H. FISCHER and MARIAN 0. 

 HooKER, 1 we must distinguish between the making of an emulsion 



1 See MARTIN H. FISCHER and MARIAN O. HOOKER, Fats and Fatty Degen- 

 eration, John Wiley and Sons, New York, 1917, where references to their earlier 

 publications may be found. 



" Both W. D. BANCROFT and G. H. A. CLOWES at the Urbana (1916) meeting 

 of the American Chemical Society, in their discussion of our own views regarding 

 the importance of colloid solvates (colloid hydrates) for the stabilization of emul- 

 sions, found in our views something irreconcilable with their notions of the im- 

 portance of interfacial films and of surface tension changes in these. While we 

 do not wish to insist upon a harmony where such may not be desired, there is, of 

 course, nothing mutually exclusive in the ideas of solvation, of changes in surface 

 tension, and at times the formation of a continuous third phase between 

 the two chief substances making up an emulsion. When "water," according to 

 our notion, becomes a "colloid hydrate," the properties of the second liquid are 

 different from those of the first, and these properties include surface tension, 

 viscosity and distribution between two phases. But, we repeat, these factors to 

 which PLATEAU, QUINCKE and PICKERING first directed attention are not by them- 

 selves able to explain all the phenomena observed. Where CLOWES holds that an 

 emulsion of oil is stabilized through sodium oleate because the substance reduces 

 the surface tension of water, we would say that stabilization has ensued because 

 the oil has been divided into a highly hydratable sodium soap. When the addi- 

 tion of calcium destroys this emulsion, it is not because of complicated changes in 

 a surface film, but simply because calcium oleate is an only slightly hydratable 



