New York Agricultural Experiment Station. 125 



in milk, although many investigators have taken up the study of 

 the nature of these cells either because of their sanitary significance 

 or because of their connection with the processes of secretion. 

 The most important of the recent papers examined are those of 

 Michaelis, 32 Lenfers, 33 Winkler, 34 and Ernst. 35 These papers deal 

 largely with the histology of the udder and the physiology of milk 

 secretion and give extensive bibliographies by means of which other 

 papers dealing with these questions can be found. A recent paper 

 by Skar 36 discusses the relation of these cells to the presence of 

 reductase. 



The results of these investigations may be summarized as 

 follows : 



1. Normal milk contains a variable number of tissue cells which 

 are probably of two kinds: (a) Leucocytes (white blood corpuscles) 

 which have passed through the epithelial lining of the alveolus. 

 Under normal conditions these are not pus cells any more than 

 leucocytes in the lymph and blood, saliva and other secretions are 

 pus cells, (b) Cell debris derived from the epithelial lining of the 

 alveoli and ducts of the udder consisting of nuclei and other frag- 

 ments of cells, and entire cells. 37 



2. These tissue cells are practically absent in the milk of some 

 cows but are normally present in the milk of the majority of cows 

 in numbers which may reach into the hundreds of thousands or 

 millions per cubic centimeter. 



3. Free epithelial nuclei and single epithelial cells are apparently 

 found frequently. Rarely groups of epithelial cells may be found 

 just as they were discharged from the lining of the alveolus. 



32 Michaelis, L. Beitrage zur Kenntniss der Milchsecretion. Arch. Mikr. Ana*. 



u. Entwickl, 55 : 711-747, 1898. 

 33 Lenfers, P. Zur Histologic der MilchdriisedesRindes. Ztschr .Fleisch- u. Milchhyg ., 



17 : 340-350, 383-390, 424-429, 1907. 



34 Winkler, W. Die Milchbildung und die mikroskopische Milchprufung. Ztschr. f. 



Landwirtsch. Versuchsw. Oesterreich, 1 1 : 562-630, 1908. 



35 Ernst, W. Ueber Milchstreptokokken und Streptokokkenmastitis. Monatsh.J. 



prakt. Tierheilk., 20 : 414-435, 498-518, 1909, 21 : 55-89, 1909. 



36 Skar, O. Verhalten der Leukozyten der Milch bei der Methylenblau- Reductase- 



probe. Ztschr. Fleisch- u. Milchhyg., 23 : 442-447, 1913. 



37 The strongest opponents of the idea that some of these cells are leucocytes are 

 Winkler and Hewlett, Villar and Revis, all of whom believe that the cells in milk 

 are of epithelial origin. The evidence which they produce to support their views is 

 far from convincing when carefully analyzed. Their interpretation of the nature of 

 the polynuclear cells as epithelial is so unusual that it needs much more conclusive 

 evidence before it can be accepted. 



