62 MILK 



capsule, thus enriching the buttermilk. Richmond argues against 

 Storch's theory, holding that if the latter's view were correct the 

 ratio of plasma solids to water in cream would differ from the 

 ratio in milk. He has shown, however, that this ratio is the same. 

 In addition, the stained area around the globules may be only a 

 condensed solution of solids due to surface attraction. This view 

 is supported by the fact that the stain is the most intense near 

 the surface of the globule and gradually fades away, while a real 

 capsule would stain more distinctly. 



Since it is obviously difficult to obtain globules which are com- 

 pletely free from adhering plasma, it is impossible to decide the 

 question of the existence of a capsule or membrane with cer- 

 tainty in the present state of our knowledge. However, the homo- 

 genizing machine breaks up fat globules into very minute ones, 

 and it is not possible to make butter from homogenized cream. 

 The fine globules of homogenized cream do not rise, and it does 

 not seem possible that membranes of any kind are formed in the 

 homogenizing process. The homogenized globules remain sus- 

 pended without noticeable change and, therefore, the assumption 

 of a membrane is superfluous to explain the emulsion of fat in 

 milk. Probably surface tension is an important factor in keep- 

 ing the globules in suspension. 



Fischer and Hooker, who have investigated the conditions 

 governing the formation of emulsions, have stated that different 

 ■factors work together in producing and stabilizing an emulsion. 

 These factors are surface tension, viscosity of the dispersing me- 

 dium, and an encircling film formed of a third substance between 

 oil and dispersing medium. These factors may differ in different 

 emulsions and in the same emulsion under different circumstances. 

 The dispersing agent— the water — is all used up in the formation 

 of a colloid hydration compound. An emulsion is not a subdivi- 

 sion of oil in water, but one of oil in a hydrated colloid. Caseia 

 is a stabilizing agent. It does not absorb much water in neutral 

 solution, but if an alkaU is added it develops marked hydrophihc 

 properties and becomes one of the best stabiUzing agents known 

 for emulsions. Acid also converts neutral casein into a hydro- 

 philic colloid which works as well as alkaline casein. 



Colostrum 



Colostrum is a viscous,' sticky, yellow fluid, the secretion of the 

 days immediately before and after parturition. The specific grav- 

 ity of colostrum is more variable than that of normal milk. The 

 following figures show the limits of variability: 



