172 CELLS, DIRT AND DEBRIS 



although on dividing, they may appear as polymorphonuclears 

 it is inconceivable that they should divide at such a rate as to 

 produce 500,000 per c.cm. There are also certain histological 

 characteristics that differentiate nucleated epithelial cells and 

 mononuclear leucocytes. 



The views of those who regard the cells found in milk as 

 mixtures of blood and epithelial cells, which is the more gen- 

 erally accepted explanation, are well set forth in a recent book 

 by Ernst * in which the histological characters of the cells are 

 treated " in extenso." 



According to Ernst the cells are of dual origin, (a) Epi- 

 thelial cells derived from the tissue lining the ducts and from the 

 secretory glands and, 



(6) Leucocytes which have passed through the walls of the 

 capillaries and lymphatics and finally obtained access to the 

 gland secretion. This would appear to be normal process in 

 all secretory glands. Under special stimulation, either from 

 mechanical or pathological causes, the number and nature of 

 the cells may undergo radical changes depending upon the 

 nature and extent of the stimulation. This affords a rational 

 explanation of the diversified cells found in milk and alterations 

 in their relative proportions under varying conditions. A 

 general description of the cells usually foimd in milk follows. 



Epithelial Cells, (a) From compound epithehum: these 

 are found as small platelets often folded in so many various ways 

 that the original shape of the cell is entirely obscured. They 

 are most numerous during the early period of the lactation and 

 are due to the mechanical stimulation of the teats by milking. 



(6) From the milk cistern; usually oval or rectangular in 

 shape, frequently elongated to a point along the longitudinal 

 axis and having an oval nucleus. In normal milk they are 

 usually found singly but increased desquamation produced 

 by stimulation may cause masses of cells to appear arranged like 

 the petals of a flower round a common centre. 



(c) From secretory ducts and alveoli: these vary in size accord- 

 ing to the number of fat globules they contain (5 to 45 fi) and 



