1037 



GLAND. 



GLAND. 



1038 



and the villi become flaccid. The function of the villi now ceases till 

 they are again roused into action by another flow of chyme along the 

 gilt. During the intervals of absorption, it becomes necessary to 

 protect the villi from the matters contained in the bowel. They had 

 thrown off their protective epithelium when required to perform 

 their functions, just as the stomach had done to afford gastric juice, 

 and the intestinal follicles to supply their peculiar secretions. In the 

 intervala of digestion the epithelium is rapidly reproduced." 



Eitremity of a villas with its absorbent vesicles distended with chyle, and 

 the trunks of iU lacteal* seen through Hi coats. Very highly magnified. 



The researches of Professor Goodsir have likewise thrown much light 

 on the general process of secretion. He shows, by an admirably 

 selected series of observations (chiefly on the lower animals), that 

 secretion is a function of the nucleated cell. 



If the membrane which lines the secreting portion of the internal 

 surface of the ink-bag of Loliijo sag'Mata (Lamarck) be carefully freed 

 from adhering secretion by washing, it will be found to consist 

 almost entirely of nucleated cells, of a dark brown or black colour. 

 These cellg are spherical or ovidal. Their nuclei consist of cells 

 grouped together in a mass. Between these composite nuclei and the 

 walls of their containing cells is a fluid of a dark brown colour. 

 ThU fluid resembles in every respect the secretion of the ink-bag 

 itself. It renders each cell prominent and turgid, and is the cause of 

 its dark colour. 



The dilated terminal extremities of the ducts in the liver of Helix 

 aperia (Mttller) contain a mass of cells. If one of these cells be 

 isolated and examined, it presents a nucleus consisting of one or 

 more cells. Between the nucleus and the wall of the containing cell 

 is a fluid of an amber tint, and floating in this fluid are a few oil- 

 globules. Thia fluid differs in no respect from the bile as found in 

 the ducts of the gland. The liver of Modiola rufgari* (Fleming) 

 contains masses of spherical cells. Between the nucleus and the wall of 

 each of these cells a light-brown fluid is situated, bearing a close resem- 

 blance to the bile in the gastro-hepatic pouches. The nucleated cells 

 which are arranged around the gastro-hepatic pouches of Pecten 

 opercularii are irregular in shape, and distended with a fluid resem- 

 bling the bile. The hepatic organ which is situated in the loop of 

 intestine of Pirena prunum (Fleming) consists of a mass of nucleated 

 cello. These cells are collected in groups in the interior of larger 

 cells or vesicles. These nucleated cells are filled with a light-brown 

 bilious fluid. The hepatic organ situated in the midst of the repro- 

 ductive apparatus, and in the loop of the intestine of Phallnsia, 

 vulyarin (Forbes and Goodsir), consists of a number of vesicles, and 

 each vesicle contains a dark-brown bilious fluid. 



The hepatic caeca in the liver of Patella vulgata contains vesicles 

 inclosing a body which consists of a number of nucleated cells full of 

 a dark fluid resembling the bile. The kidney of Helix aspersa 

 (Miiller) is principally composed of numerous transparent vesicles. 

 In the centre of each vesicle is situated a cell full of a dead white 

 granular mass. This gland secretes pure uric acid. The ultimate 

 elements of the human liver are nucleated cells. Between the nucleus 

 and the cell-wall is a light brown fluid with one or two oil globules 

 floating in it. The vesicular cseca in the testicle of Squalus comubicus 

 contain nucleated cells, which ultimately exhibit in their interior 

 bundles of spermatozoa. The generative caeca of Echiurus vutgaris 

 (Lamarck) contain cells full of minute spermatozoa. Aply&ia punctata 

 secretes from the edge and internal surface of 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 the Janlhina frayilis (Lamarck), one of the animals which 

 supplied the Tyrian dye, secretes 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 

 nucleated cells. These cells are generally ovoidal, and rather transpa- 

 rent. Between the nucleus and the cell-wall of each a quantity of 

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

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



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 destined 



to produce. Mr. Goodsir names 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 limits, 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 iu 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 primary 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 secretion 

 on the contrary, a repulsive, the one centripetal, the other centrifugal, 

 they are both centripetal. Even in their latter stages the two pro- 

 cesses, growth and secretion, do not differ. The primary formative 

 cell after becoming distended with its peculiar nutritive matter, in 

 some instances changes its form according to certain laws ; and then, 

 after a longer or shorter period, dissolves and disappears iu the inter- 

 cellular space in which it is situated ; its materials passing into the 

 circulating system if it be an internal cell, and being merely thrown 

 off if it be an external cell. The primary secreting cell, again, after 

 distenion with its secretion does not change its form so much as 

 certain of the formative cells, but the subsequent stages are identical 

 with those of the latter. It bursts or dissolves, and throws out its 

 contents either into ducts or gland-cavities. 



The general fact of every secretion being formed within cells 

 explains a difficulty which has hitherto puzzled physiologists, namely, 

 why a secretion should only be poured out on the free surface of a 

 gland-duct, or secreting membrane. We have attempted to illustrate 

 Mr. Goodsir's views by the accompanying figures : 



1. Cells from the kidney of Helix aspersa. The contained secretion is dead, 

 white and presents a chalky appearance. 



2. Cells from the ink-bag of Loligo sagitta. 



3. Cells from the liver of the Patella nilgata. In this instance the bile is 

 contained in the cavities of the secondary cells, which constitute the nucleus of 

 the primary cell. 



4. Cells from the mamma of a bitch. In addition to their nuclei these cells 

 contain milk-globules. 



After describing the development of glandular tissue Professor 

 Goodsir concludes his paper on this subject with the following 

 remarks : 



" It appears to be highly probable therefore that a gland is origi- 

 nally a mass of nucleated cells, the progeny of one or more parent 

 cells ; that the membrane in connection with the embryo gland may 

 or may not, according to the case, send a portion of the membrane in 

 the form of a hollow cone into the mass ; but whether this happens 

 or not, the extremities of the ducts are formed as closed vesicles, and 

 then nucleated cells are formed within them, and are the parents of 

 the epithelium cells of the perfect organ. Dr. Allen Thomson has 

 ascertained that the follicles of the stomach and large intestines are 

 originally closed vesicles. This would appear to show that a nucleated 

 cell is the original form of a follicle, and the source of the germinal 

 spot, which plays so important a part in its future actious. The 

 ducts of glands are therefore intercellular passages. This is an 

 important consideration, inasmuch as it ranges them in the same 

 category with the intercellular passages and secreting receptacles of 

 vegetables. 



" Since the publication of my paper on the secreting structures, in 

 the 'Transactions of the Royal Society of Edinburgh,' in 1842, I have 

 satisfied myself that I was in error in attributing to the cell-wall the 

 important function of separating and preparing the secretion con- 

 tained in the cell-cavity. The nucleus is the part which effects this. 



