136 MICROSCOPIC TESTS OF MII.K. 



tion shall occur in the case of cells in milk. It has been sug- 

 gested that this should be governed by the presence of strep- 

 tococci, or fibrin, or red blood corpuscles with the cells in 

 centrifugalized sediments. Besides the polymorphonuclears, 

 there may be demonstrated in milk sediments large and small 

 mononuclears and eosinophiles. Our knowledge of the source 

 of these cells is incomplete as yet. Boynton and Russell inde- 

 pendently have photographed sections of the functional, healthy 

 udder, and by this means have shown the presence of leuco- 

 cytes and other cells in the lumina of the lactiferous ducts in 

 contact with the epithelium. Those by Boynton appear in 

 Figs. 15 and 16. Very likely in connection with milk secretion 

 epithelial debris is extruded in milk, even though the present 

 trend of opinion denies that fat secretion is accomplished by 

 fatty degeneration with the destruction of the cell (l, 2). 

 The general leucocyte content of the blood of the cow seems to 

 bear no relation to the leucocyte count of the milk (8). 



The centrifugalized sediment of milk has been known since 

 the advent of the cream separator under the name of separator 

 slime. The mass always collecting in the bowl of the separator 

 has a disgusting appearance suggesting pus. On this account 

 some dealers clarify their milk, that is, run it through a separator 

 to remove this sediment and particles of foreign material. Here 

 again is a case where a normal milk constituent has had its 

 sanitary significance overrated, because defective tests ordi- 

 narily showed it to be preseiit in small quantity. 



Summary. Mammitis is very common among cows. The 

 majority of dairies contain cows that show active inflamma- 

 tory changes in the udder, or evidence of previous manifesta- 

 tions in the shape of indurations which might warrant the diag- 

 nosis of chronic mammitis. The discovery of diseased udders 

 in a herd after the condemnation of the mixed milk by some 

 test is therefore a fact of questionable significance in proving 

 the value of the test. 



In view of all these circumstances, it cannot be said that 

 the matter of microscopic tests for cells in milk is yet on a 

 satisfactory basis. Future work must be done on individual 

 cows in determining the border line between health and disease. 



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