646 MILK. 



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 haptogen- 

 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 albu- 

 minous membrane for the fat-globule has been generally abandoned. The observa- 

 tions 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 surrounded by a stratum of casein solution held by molecular attrac- 

 tion, and this prevents the globules from uniting with each other. Everything 

 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, 

 and BAUER has also given further proofs for the assumption of a mem- 

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

 several deductions conflicting with STORCH'S theory. If STORCH'S observa- 

 tion that the purified fat-globules contain a special protein substance 

 differing from the dissolved proteins of the milk is correct, then the 

 assumption as to a special body forming a membrane or stroma of the 

 fat-globules becomes very probable. The correctness of STORCH'S view 

 has been substantiated very recently by ABDERHALDEN and VOLTZ . 4 

 On the acid hydrolysis of the fat-globules they obtained glycocoll, which 

 is absent in the casein as well as in the lactalbumin, and this shows that the 



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; 

 Bauer, Bioch. Zeitschr. 32; Droop-Richmond, see Chem. Centralbl., 1094, 2, 356; 

 Bonnema, ibid., 1243. 



4 Zeitschr. f. pbysiol. Chem., 59. 



