154 Canadian Record of Science. 



innumerable minute globules which refract light strongly. 

 These are the globules of fat, which is not dissolved in the 

 milk, but held in suspension in it, forming what is known 

 as an emulsion. The nature of these globules and the cause 

 of their remaining suspended in the milk have given rise 

 to much controversy, and have been very carefully studied. 

 Fat is soluble in ether. But you may shake milk with 

 ether and the globules will not dissolve in it, unless you 

 add some potash or some acetic acid, and then shake with 

 ether, when they readily dissolve. So, too, if you mix 

 acetic acid with a drop of milk under the microscope, you 

 may watch the globules melt together and form larger 

 globules and irregular masses of fat. 



These globules of fat are lighter than the rest of the 

 milk, and hence on standing they rise to the surface and 

 form a layer of cream. This separation is never complete. 

 That is, the cream contains some of the other constituents 

 of the milk, and the skim milk still retains a Kttle fat — 

 about • 5 per cent. By violently agitating the cream, as 

 in churning, the fat separates in the form of butter. This 

 separation takes place more readily if the milk has become 

 just faintly acid. 



Now all these things go to show that there is some kind 

 of envelope surrounding the fat globules which protects 

 them from the action of solvents until it is itself either 

 dissolved by acid or alkali, or broken up as in the violent 

 agitation of churning. 



If the milk is heated for several hours in a little dish of 

 metal or porcelain or glass, at the temperature of boiling 

 water, the water is all driven off and the solids — the fat, 

 casein, albumen, sugar and salts — are left behind as a solid 

 residue. From this solid residue ether and other solvents 

 will readily extract the fat, so that the envelope must be 

 broken up by this process of drying also. 



Formerly it was thought that this envelope was a solid 

 skin of casein, and this idea was supported by the fact that 

 casein is soluble in acid and in alkalies. The circumstances 

 that after breaking up the globules no traces of this 

 membrane can be detected under the microscope, and that 



