SECRETING STRUCTURES. 25 



The ultimate secreting structure, then, is the primitive cell, 

 endowed with a peculiar organic agency, according to the secre- 

 tion it is destined 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 with its own peculiar 

 property, according to the organ in which it is situated. In the 

 liver it secretes bile in the mamma, milk, &c. 



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. 



The discovery of the secreting agency of the primitive cell does 

 not remove the principal mystery in which this function has 

 always been involved. One cell secretes bile, another milk ; yet 

 the one cell does not differ more in structure from the other than 

 the lining membrane of the duct of one gland from the lining 

 membrane of the duct of another. The general fact, however, 

 that the primitive cell is the ultimate secreting structure, is of 

 great value in physiological science, inasmuch as it connects 

 secretion with growth, as phenomena regulated by the same laws. 

 The force, of whatever kind it may be, which enables one pri- 

 mary formative cell to produce nerve and another muscle, by an 

 arrangement within itself of the common materials of nutrition, 

 is identical with that force which enables one primary secreting 

 cell to distend itself with bile, and another with milk. 



Instead of growth being a species of imbibing force, and secre- 

 tion on the the contrary a repulsive, the one centripetal, the 

 other centrifugal, they are both centripetal. Even in their later 

 stages the two processes, growth and secretion, do not differ. 

 The primary formative cell, after becoming distended with its 

 peculiar nutritive matter, in some instances changes its form 



