THE PHYSICAL PROPERTIES OF MILK 57 



Some milk producers pass the milk through a cream separator in 

 order to remove dirt and then mix the cream and skimmed milk 

 again. However, the mixed product does not yield as much cream 

 as the original milk. 



Cellular Elements in Milk 



The cellular elements in milk originate from several sources. 

 They are derived from the circulation, from the secreting glands 

 and from the membranes of the ducts, the cistern, and the teats 

 (Fig. 19). 



al J 



Fig. 19. — Smear from sediment of milk. Epithelial cells from teat duct (Ernst) . 



During the manipulation of milking epithelial cells are de- 

 tached from the teat and the cistern. Those from the teat appear 

 as folded platelets, as has been shown by Ernst, who saw the 

 same formations in scrapings from the mucous membrane of the 

 teat ducts. Cells from the mucous membrane of the cistern are 

 oval or four cornered, are drawn out at the base, and have oval 

 nuclei. 



Cells from the secretary ducts and alveoli contain fat droplets 

 whose size determines the size of the cells (Figs. 20, 21). Usually 

 nuclei appear. These cells are the large colostrum corpuscles and 

 are of epithelial origin, as shown by their structure and staining 

 properties. They are present in large numbers at the commence- 

 ment of lactation and reappear at its close. They also reappear 



