24 SECRETING STRUCTURES. 



its mantle a quantity of purple fluid. The secreting surface of 

 the mantle consists of an arrangement of spherical nucleated 

 cells. These cells are distended with a dark purple matter. 



The edge and internal surface of the mantle of Janthina fra- 

 gilis (Lamark), the animal which supplied the Tyrian dye, se- 

 cretes a deep bluish purple fluid. The secreting surface consists 

 of a layer of nucleated cells, distended with a dark purple 

 matter. 



If an ultimate acinus of the mammary gland of the bitch be 

 examined during lactation, it is seen to contain a mass of nu- 

 cleated cells. These cells are generally ovoidal, and rather trans- 

 parent. Between the nucleus and the cell wall of each, a quantity 

 of fluid is contained, and in this fluid float one, two, three or 

 more oil-like globules, exactly resembling those of the milk. 



In addition to the series of examples already given, I might 

 adduce many others to prove that secretion is a function of the 

 nucleated cell. Some secretions, indeed, are so transparent and 

 colourless, as to render ocular proof of their original formation 

 within cells impossible ; and we are not yet in possession of chemi- 

 cal tests sufficiently delicate for the detection of such minute quan- 

 tities. The examples I have selected, however, show that the most 

 important and most striking secretions are formed in this man- 

 ner. The proof of the universality of the fact, in reference to 

 the glandular structures which produce colourless secretions, can 

 only rest at present on the identity of the anatomical changes 

 which occur in their cellular elements. This part of the proof I 

 shall enter upon in another part of this chapter. 



The secretion within a primitive cell is always situated between 

 the nucleus and the cell wall, and would appear to be a product 

 of the nucleus.* 



* In the original Memoir the cell wall is stated to be the probable secreting structure. 

 " Now, as we kncfw that the nucleus is the reproductive organ of the cell, that it is from it, 

 as from a germinal spot, that new cells are formed, I am inclined to believe that it has 

 nothing to do with the formation of the secretion. I believe that the cell wall itself is the 

 structure, by the organic action of which each cell becomes distended with its peculiar 

 secretion, at the expense of the ordinary nutritive medium which surrounds it." Trans. 

 Roy. Soc., Edin. 1842. 



