MILK. 



coat. A true membrane has not been detected ; and since, when 

 no means of dissolving the albumin is resorted to for example, 

 when the milk is precipitated by carbon dioxide after the addition 

 of very little acetic acid (SOXHLET), or when it is coagulated by 

 rennet the fat can be very easily extracted by ether, the theory of a 

 special albuminous membrane for the fat-globules has been gener- 

 ally abandoned. The observations of QUINCKES on the behavior 

 of the fat-globules in an emulsion prepared with gum have led, 

 at the present time, to the conclusion that each fat-globule in the 

 milk is surrounded by a stratum of casein solution by means of 

 molecular attraction, and this prevents the globules from uniting 

 with each other. Everything that changes the physical property 

 of the casein in the milk or precipitates it must necessarily help 

 the solution of the fat in ether, and it is in this way that the alka- 

 lies, acids, and rennet work. 



If we accept this view, which requires further proof, we must not over- 

 look the fact that the fat-globules remain unchanged when the milk under 

 agitation is coagulated with rennet. In this case we find an immense amount 

 of unchanged milk-globules in the whey, and if we wish to admit of a stratum 

 of proteids around the fat-globules proceeding from the molecular attraction, 

 we must not consider that it is entirely due to casein, but also to albumin. 



If the fat-globules are filtered off and washed on a filter, we always obtain 

 (RADENHAUSEN and DANILEWSKY) after their treatment with ether a residue 

 consisting of albumin. From this behavior the deduction has been made that 

 the fat-globules, even though they have no real membrane, consist, neverthe- 

 less, of fat and albumin. The extreme difficulty of completely removing the 

 albuminous bodies of the milk by washing the fat on the filter renders it 

 necessary to exercise great caution in drawing a conclusion. The question as 

 to the composition of the milk-globules, and especially as to the possible 

 amount of albumin, cannot be decided at present. 



The milk-fat has a rather variable specific gravity, which accord- 

 ing to BOHR, is 0.949-0. 996 at 15 C. The milk-fat, which is ob- 

 tained under the name of butter, consists in great part of the 

 neutral fats palmitin, olein, and stearin. Besides these it contains, 

 as tri-glycerides, small quantities of butyric acid and caproic acid, 

 traces of caprylic and capric acids (lauric acid probably also occurs), 

 myristic and arachidic acids. Butter which has been exposed 

 to the action of sunlight contains also formic acid (DucLAUX). 

 Milk-fat also contains a small quantity of lecithin and cholesterin, 

 also a yellow coloring matter. The quantity of volatile faty acids 

 in butter is, according to DUCLAUX, on an average about 70 p. m., 

 of which 37-51 p. in. is butyric acid and 20-33 p. m. is caproic 



