FAT GLOBULES. 613 



whose diameter is 0.0024-0.0046 mm. and 0.0037 mm. as an average for 

 different kinds of animals. It is unquestionable that the milk-globules 

 contain fat, and we consider it as positive that all the milk-fat exists in 

 them. Another disputed question is whether the milk-globules consist 

 entirely of fat or whether they also contain protein. 



The observations of ASCHERSON 1 show that drops of fat, when 

 dropped in an alkaline protein solution, are covered with a fine albuminous 

 coat, a so-called haptog en-membrane. As milk on shaking with ether 

 does not give up its fat, or only very slowly in the presence of a great 

 excess of ether, and as this takes place very readily after the addition 

 of acids or alkalies, which dissolve proteins, it was formerly thought that 

 the fat-globules of the milk were enveloped in a protein coat. A true 

 membrane has not been detected; and since, when no means of dissolving 

 the protein is resorted to for example, when the milk is precipitated 

 by carbon dioxide after the addition of very little acetic acid, 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-globule has been 

 generally abandoned. The observations of QUINCKE 2 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 sur- 

 rounded by a stratum of casein solution held by molecular attraction, 

 and this prevents the globules from uniting with each other. Every- 

 thing that changes the physical condition 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 alkalies, acids, and rennet act. 



V. STORCH has shown, in opposition to these views, that the milk- 

 globules are surrounded by a membrane of a special slimy substance. 

 This substance is very insoluble, contains 14.2-14.79 per cent nitrogen, 

 .and yields a sugar, or at least a reducing substance, on boiling with 

 hydrochloric acid. It is neither casein nor lactalbumin, but it seems to 

 all appearances to be identical with the so-called " stroma substance " 

 detected by RADENHAUSEN and DANILEWSKY. STORCH was able to 

 show, by staining the fat-globules with certain dyes, that this substance 

 enveloped them like a membrane. Recently VOLTZ has given further 

 proofs of the view that the fat-globules probably have a membrane, 

 which in his opinion is a very labile formation of variable composition. 

 DROOP-RICHMOND and BONNEMA, S on the other hand, present several 

 deductions conflicting with STORCH'S theory. If STORCH'S observation 



1 Arch. f. Anat. u. Physiol., 1840. 



2 Pfliiger's Arch., 19. 



3 V. Storch, see Maly's Jahresber., 27; Radenhausen and Danilewsky, Forschungen 

 -auf dem Gebiete der Viehhaltung (Bremen, 1880), Heft 9; Voltz, Pfliiger's Arch., 102; 

 Droop-Richmond, see Chem. Centralbl., 1904, 2, 356; Bonnema, ibid., 1243. 



