1112 



THYROID GLAND. 



the limitary tissue is discoverable nowhere, 

 not even surrounding those curious spherical 

 masses of nuclei the white corpuscles of Mal- 

 pighi. The only circumstance I know of, 

 which seems to indicate that even in the spleen 

 a kind of secretory action does occasionally 

 take place, is, that there frequently occur, in 

 the parenchyma, some peculiar yellow cor- 

 puscles, which are most abundant in fishes, 

 and of which I gave a detailed account some 

 years ago. The very presence, however, of these 

 (for they are by no means constant), as well as 

 their condition, argue strongly that secretion is 

 not the appointed function of the splenic 

 parenchyma. From this, the last and lowest 

 of the ductless glands, we descend to erectile 

 tissue, in which the venous portion of the 

 sanguiferous system is even more highly de- 

 veloped than in the spleen, and where the 

 intervening parenchyma is still further reduced 

 in quantity; yet, from the phenomenon of 

 afflux of blood to the part, it must be regarded, 

 I think, as exerting an attractive force, as is 

 unquestionably the case in the spleen.* 



Returning from this digression to the con- 

 sideration of the thyroid, we may lay it down 

 as fully established, that it is a gland whose 

 secretion is formed, and collects, in closed 

 cavities. Now from this fact we are able 

 easily to deduce another, vi/., that the secre- 

 tion when formed is capable of being absorbed 

 from the receptacuiar cavities ; for otherwise 

 these would go on enlarging and distending 

 themselves indefinitely, as in fact they do 

 under certain morbid conditions. But, though 

 there may be various causes concerned in 

 the production of bronchocele, yet I think it 

 must be regarded as proved, by Mr. M'Clellan's 

 inquiries, that certain waters are adequate of 

 themselves to produce this disease ; it would 

 appear that when they are drunk, some in- 

 gredient or principle is supplied to the blood, 

 which, being in excess, is straightway elimi- 

 mated by the epithelium of the glandular 

 cavities of the thyroid, and thus collects in, 

 and distends them. If a patient in whom this 

 has occurred be removed from using this 

 unwholesome water, and if the natural ab- 

 sorbing power be aided by the influence of 

 iodine, then, the supply of the substance for 

 which the thyroid has a special attraction 

 being cut oft', the excess collected in the 

 receptacuiar cavities returns speedily to the 

 circulating current, which now, being in a 

 minus condition as to this principle, readily 

 resumes it. In such cases there seems, in 

 fact, to take place a very analogous process 

 to that which occurs in ordinary fattening 

 and emaciation ; if an excess of oily matter 

 exist in the blood, old fat vesicles enlarge, and 

 new ones are formed ; if the reverse is the 



* The well marked variation in size of the spleen 

 at different times proves, I think beyond doubt, 

 that it exerts an actively attracting force on the 

 blood which traverses it ; else what possible reason 

 can be given for its containing much more blood at 

 one time than at another ? No contractile tissue 

 exists here which can be supposed to obstruct the 

 returning current by the splenic vein. 



case, the oil in the fat cells is readily absorbed 

 into the blood circulating in the capillary 

 loops around them. 



The condition in which the epithelium of 

 the thyroideal cavities is usually found is 

 worth observing, and seems susceptible of a 

 probable interpretation. It may be stated as 

 a pretty well established fact, that the nucleus 

 of a cell is the essential part, that in it resides 

 that influence, or is developed that force, which 

 produces all the phenomena of growth and 

 assimilation ; that, so long as the nucleus 

 persists, the energy of the cell, if one has been 

 formed, continues to be manifested ; but, if it 

 has disappeared, the active life of the cell is 

 at an end. It is also certain that the comple- 

 tion of a cell, i.e. its being surrounded by an 

 envelope, is by no mea*is an essential circum- 

 stance ; that all the purposes of cell life may 

 be effected by the mere aggregation of granular 

 matter around a nucleus ; that, in fact, the 

 cell wall or envelope is of no importance, or 

 but very little, in the metabolic changes which 

 are produced, and that its presence, when it 

 exists, seems merely to denote a certain per- 

 manence of duration in the particle. Many 

 examples of the correctness of these state- 

 ments, will occur to every one who is in the 

 habit of examining the glandular organs in 

 man or the lower animals. I believe we 

 may also advance a step beyond these doc- 

 trines, and regard it as very probable that, 

 when we find an epithelial structure con- 

 sisting principally of bare nuclei, with but 

 a scanty interposed quantity of granular 

 matter, the secreting action there effected is 

 of a rapid and simple kind ; the destined pro- 

 duct being quickly formed and thrown off, and 

 not slowly evolved within the chamber of 

 a cell. The following instances may be re- 

 ferred to, as illustrating the extreme varieties 

 of secretory action in reference to this par- 

 ticular. The cells in which the spermatozoa 

 are formed must be of considerable per- 

 manence, the development of the filaments 

 taking place gradually, and in one instance, as 

 Mr. Goodsir has shown, only being completed 

 in the spermatheca of the female. The biliary 

 cells of various annelida are at first filled with 

 pale granular contents ; but gradually these 

 are replaced by the characteristic molecules 

 with which the cell becomes at last distended, 

 and thus remains, often for a long time. The 

 cells of the kidney of the common snail, 

 which are very perfectly formed, enclose, 

 within a well marked envelope, an opaque 

 white mass of uric acid, which, after a long 

 time, may increase to such a degree as com- 

 pletely to fill the cell. These cells are very 

 permanent.* 



In contrast to these instances, wherein 

 complex and elaborate products are formed in 

 complete cells by a secretory action of a slow 

 and deliberate character, we may refer to (1) 



* I preserved some snails in a box for about a 

 year they remained in a perfectly torpid state, and 

 took no food. The renal cells at the end of that time 

 were almost all fully distended with uric acid, while 

 usually they are not more than half full. 



