m] THE CONSTITUENTS OF MILK 21 



it has been found that the same weight of fat retards 

 more light when it is in the form of small globules 

 than when it is in the form of larger globules ; so 

 that two samples of milk, containing equal amounts 

 of fat, but the fat in the one in the form of larger 

 globules than in the other, might give different 

 results when thus tested. 



The Condition of the Fat Globules in Milk. A 

 point of the very highest interest, and one which 

 has engaged considerable attention, is the condition 

 in which these fat globules are present in milk. It 

 was till comparatively recently believed that they 

 were surrounded by a solid albuminous membrane 

 which became ruptured when milk was churned. 

 This theory seemed to derive considerable support 

 from the behaviour of the fat under different cir- 

 cumstances. For one thing, it was found almost im- 

 possible to obtain fat from milk absolutely devoid of 

 nitrogenous matter. Another reason for believing in 

 the existence of a membrane was the isolation which 

 the fatty globules maintained in the milk. If there 

 is no albuminous envelope, why do the globules not 

 coalesce ? it may be asked. A further striking anomaly 

 seemed also to point to the existence of a membrane, 

 viz. that the fat is in a liquid condition, although 

 its temperature may be far below its melting-point. 1 



1 A proof of the liquid condition of the fat in the globules at 

 even fairly low temperatures, viz. those approaching the freezing- 



