134 



MICROSCOPIC TESTS OF MILK. 



Micrococci in milk. Micrococci (staphylococci), indistin- 

 guishable from Micrococcus pyogenes, varieties au7'eus and alius, 

 are normal inhabitants of the udder. Consequently, they are 

 almost the characteristic organisms in the bacterial flora of 

 fresh milk. Their close relationship to M. pyogenes aureus 

 has been determined by thorough systematic study. They 

 have been reported under this name by numerous observers, 

 as noted in Chap. I. 



The practice of reporting on the presence of pyogenic micro- 

 cocci in centrifugalized sediments, from microscopic examin- 

 ation, is certainly not justified. 



Leucocytes in milk. Polymorphonuclear leucocytes may be 

 demonstrated in the milk of any cow and must be regarded as 

 a normal constituent of milk. As many as 200,000 per cc. in 

 the milk of a cow may be considered Common, and 500,000 

 per CC. not at all unusual. Sprague (9, 27) found the greatest 



Fig. 15. Section of udder sliozviiig epithetial cells. 



a. Epithelial cell zuhirh lias become loosened from the duct and is ready 

 to be carried out. b. Secreting epithelial cell in wall of duct, a and b 

 are of the same structure. 



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