CONTENT OF COW'S MILK n 



the milk cistern and in the teat canal, forming in the latter 

 a column of fluid. The existence of this column of fluid in 

 the teat canal has been denied by some observers, but the 

 balance of evidence is in its favour. 



In the goat only two mammary glands are present with 

 two teats. 



As regards the histological structure of the acini, three 

 layers may be distinguished : (a) a layer of epithelial cells 

 forming the glandular cells and lining the lumen of the acinus, 

 (&) a thin layer of muscle cells lying upon (c) a basement 

 membrane thin and structureless. The actual appearances to 

 be seen in microscopic preparations vary considerably ac- 

 cording to the stage of lactation. According to the gener- 

 ally accepted view, the interstitial tissue and the epithelial 

 layers are infiltrated by leucocytes during active secretion, 

 many of which find their way into the lumen of the acini. 

 These, together with the epithelial cells, are found in the 

 milk. 



According to Winkler, a further layer of cells is present 

 between the muscle cell layer and the epithelial cells. This 

 he calls the germinal cell layer and considers it as the source 

 from which the epithelial cells of the gland are constantly 

 renewed. 



The histological structure throws light upon the cellular 

 content of milk. Cellular elements are always to be found 

 in milk even from the healthiest animals, but marked 

 variations are met with, both as regards their numbers and 

 the varieties present. The cellular elements are usually 

 spoken of as leucocytes, but since it is probable that not 

 all are actual white corpuscles, although many of them are 

 of that nature, it is perhaps better to speak of cellular content 

 rather than of leucocytes. 



From his own investigations, 1 the writer classified the 

 cells found in milk into three groups (Fig. 2), although occasion- 

 ally cells are found which could not be accurately placed in 

 any one of these three groups. 



(a) Polymorphonuclear Cells. Medium - sized, with a 

 diameter varying from about 7'5//, to 10/*. The protoplasm of 

 the cell is only seen with difficulty, but the nucleus stains 



1 Report of Medical Officer, Local Government Board, 1906-7, p. 205. 



