s^:uRETI^'li structures. 417 



structures wliicli produce colourless secretions, cuu only rest 

 at present on the identity of the anatomical cliange.s which 

 occur in their cellukir 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.* 



The ultimate secreting structure, then, is the primitive 

 cell, endowed with a peculiar organic agency, according to the 

 secretion it is destinetl to produce. I shall henceforward 

 name it the primary secreting cell. It consists, like other 

 primitive cells, of three parts — the nucleus, the cell-wall, and 

 the cavity. The nucleus is its generative organ, and may or 

 may not, according to circumstances, become developed into 

 young cells. The cavity is the receptacle in which the 

 secretion is retained till the quantity has reached its proper 

 limit, and till the period has arrived for its discharge. 



Each primary secreting cell is endowed Mith its own 

 peculiar property, according to the organ in which it is 

 situated. In the liver it secretes bile — iu the mamma, milk, 

 etc. 



The primary secreting cells of some glands have, merely 

 to separate from the nutritive medium a greater or less 

 number of matters already existing in it. Other primary 

 secreting cells are endowed with the more exalted property 

 of elaborating from the nutritive medium matters which do 

 not exist in it. 



* In the original Memoir tlip coil-wall is stated to be the probable .secreting 

 stnicture. "Now, a.s we know that the nucleus is the rcproluctive 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 tlu' 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 onlinary nutritive medium which surrounds it" — Trans. Bfy. 

 Soc. Edin. 1842. 



2 E 



