SECRETION. 



455 



takes place from the caecal extremities ; and 

 Prof. Goodsir considers that they originate 

 in a " germinal spot," which is the persistent 

 nucleus of the parent cell, whose enlargement 

 and connection with the gland forms the 

 follicle. Growth in glands of this kind is 

 regulated, according to him, by the following 

 laws : 



" 1st. Each follicle is virtually permanent, 

 but actually in a constant state of develop- 

 ment and growth. 



" 2d. This growth is contemporaneous with 

 the function of the gland ; that function being 

 merely a part of the growth, and a conse- 

 quence of the circumstances under which it 

 occurs. 



" 3d. The vital action of some follicles is 

 continuous, the germinal spot in each never 

 ceasing to develope nucleated cells, which 

 take on the action of, and become, primaiy 

 secreting cells, as they advance along the 

 follicle. The action of other follicles is 

 periodical. 



" 4th. The wall, or germinal membrane, of 

 the follicle is also (probably) in a state of 

 progressive growth, acquiring additions to its 

 length at the blind extremity, and becoming 

 absorbed at its attached extremity. A pro- 

 gressive growth of this kind would account 

 for the steady advance of its attached con- 

 tents, and would also place the wall of the 

 follicle in the same category with the primary 

 vesicle, germinal membrane, or wail of the 

 acinus, in the vesicular glands. 



" 5th. The primary secreting cells of the 

 follicle are not always isolated. They are 

 sometimes arranged in groups ; and when 

 they are so, each group is enclosed within its 

 parent-cell, the group of cells advancing in de- 

 velopment according to its position in the 

 follicle, but never exceeding a particular size 

 in each follicle."* 



Prof. Goodsir further expresses the opi- 

 nion, that there is an order of glands with 

 very much elongafcd ducts, which do not 

 possess " germinal spots " in particular situ- 

 ations, but in which these spots are diffused 

 more uniformly over the whole internal sur- 

 face of the tubes. To this order he refers the 

 kidney in Man and the higher Vertebrata. 



We have thought it right to give Prof. 

 Goodsir's statements in full, as being in the 

 main unquestionably correct ; but we must 

 express our own doubts as to that part of the 

 doctrine which relates to the production of 

 the secreting cells from distinct " germinal 

 centres." We have examined a great number 

 of membranes bearing an epithelial covering, 

 without being able to discern these ; and our 

 own impression is, that the membrane itself 

 is in a continual state of change, deriving 

 from the blood-vessel, on the one side, the 

 elements of the new growth, and yielding 

 these up on the other. 



Of the first development of secreting struc- 

 tures, a partial account was formerly given 

 (see GLAND) ; and as this is on the whole in 



* Op. cit. p. 31. 



conformity with our present views, it is only 

 requisite to add here the principal facts, as- 

 certained by microscopic research since that 

 article was written. 



The "plastic mass" of which the entire 

 gland consists in its early condition, is now 

 known to be composed of nucleated cells, 

 which appear to be the parent-cells within 

 which the true secreting cells are afterwards 

 to be formed ; these parent-cells themselves 

 becoming the vesicles or follicles of the gland, 

 by the establishment of communications be- 

 tween their cavities and the branches of the 

 duct. It seems probable that some of the 

 original component cells of the gland coalesce 

 or break down altogether, so as to form the 

 smaller ducts, the development of which has 

 been observed to be quite independent of the 

 protrusion of the principal duct, and of its 

 primary branches, from the cavity of which it 

 is a diverticulum. These last are properly 

 intercellular passages; which, as Prof. Good- 

 sir justly observes, " is an important consider- 

 ation, inasmuch as it ranges them in the same 

 category with the intercellular passages and 

 secreting receptacles of vegetables." 



Sources of the demand for the secreting 

 function. We must now consider in more 

 detail, the causes which render the perform- 

 ance of this function essential to the active 

 existence of every living being. 



1. In the first place, nearly all the solids 

 and fluids of the animal body are liable to 

 continual decomposition and decay, in virtue 

 of their peculiar chemical composition. That 

 the living state antagonises this decay, and 

 that decomposition can only take place after 

 death, is a doctrine which long held undis- 

 puted sway in physiological science, but 

 which is now generally admitted to be com- 

 pletely untenable. The resistance to decay 

 which living organised structures present, is 

 rather apparent than real; for it only con- 

 tinues so long as the circulating current con- 

 tinues to pass through or near them, carrying 

 off the products of incipient decomposition, 

 and replacing these by matter that is newly 

 organised. 



2. In the second place, a continual decom- 

 position and decay of an organised fabric is 

 involved in its mere vegetative existence. For 

 every portion of it has an individual and 

 independent life, and a limited duration of its 

 own : each part, like the simple isolated cell 

 of the lowest Cryptogamia, grows from a 

 germ, arrives at maturity, and finally dies and 

 decays ; its debris being directly cast off, if the 

 organ be external ; but being taken again into 

 the current of the circulation, to be eliminated 

 by another channel, if the part have no direct 

 communication with the surface of the body.* 

 Perhaps the most obvious example of this 

 general fact is presented to us in the vegetable 



* The author believes that he may claim the 

 credit of having been the first to enunciate this 

 doctrine in definite terms, and as more than a mere 

 hypothesis. (See Mr. Paget's Lectures on Nutrition, 

 &c. Medical Gazette, 1847.) 



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