SECRETION. 



453 



When the foregoing facts are duly weighed, 

 the conclusion seems irresistible, that the cells 

 containing the biliary matter are the only in- 

 variable constituents of the hepatic appa- 

 ratus ; and that the manner in which these 

 cells are arranged, and brought into relation 

 with the blood-vessels, may vary indefinitely 

 without producing any change in the charac- 

 ter of the product. Consequently we cannot 

 but look upon the biliary cells as the essential 

 portion of the secreting structure ; and we 

 must, in like manner, consider their agency as 

 the essential part of the secretory function. 



The same result has been obtained in all 

 other cases in which the character of the se- 

 creted product is such, that it can be de- 

 tected, when in a finely divided state, by the 

 assistance of the microscope. Thus Prof. 

 Goodsir has shown* that the pigmentary 

 matter of the "ink" of the cuttle-fish is con- 

 tained within the cells that line the ink-bag ; 

 that the purple fluid secreted from the edge 

 and internal surface of the mantle of lanthina 

 fragilis (which is supposed to have furnished 

 the Tyrian dye) is contained within a layer 

 of nucleated cells situated on the secreting 

 surface ; and that a fluid resembling milk may 

 be found in the cells contained within the 

 ultimate follicles of the mammary gland in a 

 lactating animal. We seem perfectly justified 

 in concluding, therefore, that in cases where 

 the transparency and freedom from colour of 

 the secreted product prevent our distinguish- 

 ing it in the cells of the organ by which it is 

 eliminated (as in the case of the urine), it is 

 nevertheless contained within them and eli- 

 minated by their agency. 



It would probably be too much to affirm, that 

 the elimination of the secretion always involves 

 the continual exuviation of the cells, which are 

 the instruments of the process. On the con- 

 trary, it seems probable that where the solid 

 matter of the secretion bears but a small pro- 

 portion to the liquid, and is in a state of per- 

 fect solution, the secreting cells may be con- 

 tinually drawing in their peculiar pabulum on 

 the side nearest to the capillary network, and 

 may be as constantly allowing it to transude 

 by the free surface, so as to permit its pas- 

 sage into the cavity of the tube or follicle, the 

 cells themselves remaining attached to its 

 walls, and continuing to perform this function 

 for a considerable time. Such is probably the 

 case with regard to the epithelial cells which 

 line the tubuli of the kidney, and which eli- 

 minate the secretion of urine ; and those 

 which line the tubes of the perspiratory glan- 

 dule are probably as permanent. 



In the case of cells, however, whose secre- 

 tion contains a large quantity of solid matter, 

 and especially where this is of an adipose 

 character, it seems impossible to suppose that 

 their contents can be given up, without the 

 rupture or deliquescence of the cell-walls. 

 This may take place either whilst the cells 

 are yet in the follicles within which they were 

 generated, or after they have been cast entire 



* Trans, of Royal Society of Edinburgh, 1842. 



into the ducts, or have been even conveyed 

 through them to their outlet. We have seen 

 that in the biliary follicles of the Invertebrata, 

 the discharged contents of secreting cells are 

 usually to be met with, indicating that this 

 rupture or deliquescence has taken place with- 

 in the follicles ; and this is probably the fact 

 in regard to the biliary cells in general. An 

 extreme case of another kind is furnished by 

 Mr. Harry Goodsir, in regard to the cells of 

 an organ which is essentially one of secretion 

 as to its structure, though its function has a 

 different direction ; the peculiarity of this case 

 being, that even after the complete exuviation 

 of the cells, they retain so much of inde- 

 pendent vitality, as to proceed in their own 

 development to a stage much beyond that at 

 which they were set free. The case referred to 

 is that of the seminal secretion of the deca- 

 podous crustaceans ; the cells of which, when 

 thrown out of the caeca of the testis, are very 

 immature, and undergo important changes in 

 their progress along the tubuli of that gland. 

 The final changes, however, whereby they are 

 fitted for the fertilisation of the ova, only 

 take place after they have been discharged 

 from the male organs, and have been lodged 

 in the spermotheca of the female.* 



Now in every case in which the secreted 

 product can only be given up by the rupture 

 or solution of the cell-wall, it is obvious that 

 there must be a continual succession or new 

 production of the secreting cells ; and a ques- 

 tion naturally arises as to their origin and 

 mode of development. Few facts are as yet 

 known upon this subject. It may, however, 

 be stated with some certainty, that, in many 

 of the simpler glands at least, the follicle with 

 its contained secreting cells was originally 

 a single closed cell, of which the secreting 

 cells are the progeny. This is the case with 

 the Peyerian glands, which are best known 

 to us in this condition, but which afterwards 

 open and discharge their contents into the 

 intestinal canal. Dr. Allen Thomson has ascer- 

 tained that the primitive condition of the gas- 

 tric gland also is that of a closed vesicle ; and 

 Henle has extended this view to the terminal 

 follicles of the more complex secreting glands, 

 which he considers to have originated in the 

 same condition. The observations of Prof. 

 Goodsir upon the testis of Squalus cornubicus 

 show that this is the true account of the 

 changes occurring in that organ ; the follow- 

 ing stages being distinguishable in its structure, 

 when it is in a condition of activity : 1st, 

 Isolated nucleated cells attached to the side 

 of the duct, and protruding as it were from its 

 outer membrane (fig. 321. a). 2nd, A cell 

 containing a few young cells grouped in a mass 

 within it, the parent cell presenting itself 

 more prominently on the side of the duct. 

 3d, A cell attached by a pedicle to the duct, 

 the pedicle being tubular, and communicating 

 with the duct ; the cell itself being pyriform, 

 but closed and full of nucleated cells (6). 



* Anatomical and Pathological Observation*, 

 p. 39. - 



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