PHYSICAL PROPERTIES OF MILK 93 



normal milk the fat globules, in place of being homogeneously 

 distributed throughout the microscopic field, are grouped 

 in part in irregular but well-defined masses. But not all 

 of the fat globules are included in these fat aggregations. 

 Some of the globules remain isolated and distinct, although 

 there is a marked tendency in cover-glass preparations, owing 

 to capillary currents, for these individual globules to be 

 caught in these irregular groupings. The matrix that holds 

 these fat globules together is under the microscope practically 

 transparent, but by watching these currents with their floating 

 fat globules, the irregular outline of the fat clots can be perceived. 

 In these clots it will be observed that the individual fat globules 

 retain their spherical form and do not coalesce, as is the case in 

 incipient churning. 



The nature of the substance that acts in the capacity of clot 

 binders is not well understood. Babcock ascribed this effect to 

 the presence of a small quantity of lacto-fibrin which he thought 

 acted in a manner similar to blood fibrin. His proof for the 

 presence of fibrin was not direct, although numerous physical 

 and chemical reactions were noted that were identical with those 

 found with blood fibrin. 



The microscopic appearance of milk or cream that has 

 been heated above 65 C. (149 F.) is totally different. Not 

 only is this true with pasteurized milk, but sterilized or 

 boiled milk as well as condensed milk likewise present a 

 similar microscopic appearance. In these cases the fat 

 globules are homogeneously distributed throughout the micro- 

 scopic field. The fat aggregations that are so characteristic 

 of the preparations of normal milk and cream are here entirely 

 lacking. 



Hundreds of preparations have been made of both pasteurized 

 milk and cream from individual and mixed milks, and in no case 

 have we found any exception to this condition. This phenome- 

 non is certainly coincident with the change in consistency, and 



