COMPOSITION OF MILK. 9 



and the total fat made up of a mechanical mixture of these 

 and the remainder of the fats in butter-fat. 



Richmond and other authors believe that fat probably exists 

 in milk chemically, as first mentioned and illustrated; because, 

 if the fat were a mixture of glycerine tributyrate with other 

 glycerides of fat, butyrin or glycerol tributyrate could be 

 dissolved out by the use of alcohol. But this is not the case. 

 Moreover, if butyrin existed separately in milk, it would be 

 possible to distill it off under reduced pressure. This cannot be 

 done. 



Theory in Regard to Films Enveloping Fat-globules. The 

 extreme minuteness of the fat-globules in milk renders it almost 

 impossible to determine by direct microscopical observation 

 whether there is a membrane around each globule or not. 

 Fleischmann and Lloyd assert that, so far as they were able 

 to detect, there is no real membrane surrounding each globule. 



The theory generally accepted in the past was that the 

 only film surrounding the fat-globules was simply due to sur- 

 face tension, or to the fact that the molecules of the fat have 

 a greater attraction for themselves than they have for the 

 molecules of the serum, in which they are held in suspension. 

 In support of this two things are considered : 



(1) The natural milk-fat may be removed from milk and 

 artificial fat substituted in its place. The resultant milk has 

 characteristics similar to milk containing normal fat; that 

 is, the emulsion which milk forms with the artificial fat is ap- 

 parently like that formed with the natural fat. 



(2) If there were a special albuminous membrane around 

 each fat-globule, cream should contain a higher percentage 

 of albuminoids than milk. This, Richmond maintains, is not so. 



Dr. Storch concludes from extensive researches that there 

 is a gelatinous membrane enveloping the fat-globules. His 

 conclusions are based mainly upon the first three reasons 

 given below. The other facts mentioned also support his 

 conclusions : 



(1) When milk has been stained with ammoniacal picro- 



