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- 
