The Normal Mode of Secretion in 
 the Thyroid (Hand 
 
 R, R. BENSLEY 
 
 From tlif Hull Laboratory of Anatomy, University 
 of Chicago 
 
 Reprinted from THE AMERICAN JOURNAL OF ANATOMY, 
 Vol. 19. No. 1, January. 1916 
 

Reprinted from THE AMERICAN JOURNAL OF ANATOMY, VOL. 19, No. 1 
 January, 1916 
 
 THE NORMAL MODE OF SECRETION IN THE 
 THYROID GLAND 
 
 R. R. , 
 
 From the Hull Laboratory of Anatomy, ' University of Chicago 
 
 ONE PLATE IN COLOR 
 
 In the glands of the alimentary canal the process of secretion is 
 associated with definite changes in the structure of the secreting 
 cells, and with the accumulation in them of products, granular 
 or otherwise, which may be interpreted as the organic antece- 
 dents of the secretion itself. Even in some of the internal secret- 
 ing glands, as, for example, the islets of Langerhans of the pan- 
 creas, functioning is associated with the storage or exhaustion of 
 intracellular products which may be similarly interpreted. By 
 means of these secretion antecedents an observer, who has, by 
 experiment and observation, acquainted himself with the secre- 
 tory mode, may form an estimate of the secretory potential at 
 the time of observation. 
 
 In the thyroid gland, on the other hand, the search for such 
 evidences of secretory activity, has been, as regards the nature 
 of the intracellular secretion antecedents, of so contradictory a 
 nature, and of such doubtful functional import, that, at present, 
 we are unable to state from the examination of a thyroid gland 
 whether the gland was active or inactive. Accordingly, differ- 
 ent observers, as, for example, in Grave's disease, in discuss- 
 ing the same results, have arrived at diametrically opposed 
 conclusions. 
 
 One of the features of the thyroid gland, in particular, which 
 baffled interpretation was the presence in it of a storage product, 
 the so-called colloid, the route and rate of resorption of which 
 have remained problematical, though chemical and physiologi- 
 cal studies indicated that it contained the physiologically active 
 
 37 
 
 THE AMERICAN JOURNAL OF ANATOMY, VOL. 19, NO. 1 
 
 '37091 
 
38 R. R. BENSLEY 
 
 thyroid substances. Some observers have even doubted the 
 resorption of this material, and have suggested that the function 
 of the thyroid gland was primarily to withdraw toxic substances 
 from the blood. Others have conceived the colloid as a sort of 
 menstruum in which the real thyroid secretion was received and 
 from whidji.'it might bfc -withdrawn without visible change in the 
 colloid itself. ..Siifl others' h.ave held the view that the colloid 
 was tbe*.]jekl: ^rgti^n of ,-the Jhyroid gland and that the normal 
 mechanism of thyroid secretion was by this indirect route, first 
 secreting into the centre of the follicle, and then withdrawing 
 this ware-housed material, as functional needs required, by some 
 unknown method and route. 
 
 The determination of the true significance of the colloid in the 
 secretory cycle of the gland, and of the ways in which it is formed, 
 and of its intracellular antecedents, is of fundamental importance 
 in the physiology and pathology of the thyroid gland. The con- 
 viction that it is by this indirect method that the thyroid gland 
 produces its internal secretion lies at the bottom of all of our 
 more or less speculative interpretations of pathological conditions, 
 and in view of the strong physiological evidence supporting this 
 conviction few have had the courage to question its accuracy. 
 Many authors have tried nevertheless to influence experimentally 
 the rate of secretion in the gland, and to read in the changes so 
 produced the true history of its secretory process. In this way 
 many interesting facts have been discovered, which at present 
 seem to some extent contradictory of one another, but which 
 nevertheless must be found to be in accord when the true history 
 of the process is revealed. 
 
 Our earliest knowledge as to the origin of the intrafollicular 
 colloid of the ' thyroid gland is due to Biondi and Langendorff. 
 Biondi ('89) showed, that this substance was a true product of 
 the secretory activity of the thyroid epithelial cells, inasmuch 
 as he found globules of similarly staining substances in the cells 
 themselves. He conceived the process of secretion as follows: 
 the cells of the thyroid gland produce the colloid, .since one can 
 see in them little globules having the same microchemical reac- 
 tions; the vesicle has a tendency to increase in size partly by 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 39 
 
 multiplication of the epithelial cells, partly by increase of the col- 
 loid; after filling itself the vesicle discharges into the nearest 
 lymphatic vessel; finally the collapsed vesicle disposes itself in the 
 form of a number of little acini which repeat the process. 
 
 Langendorff ('89) using the method of comparative study for 
 the elucidation of the secretory process in the cells of the thy- 
 roid gland, reached conclusions which, in some respects, confirm 
 and extend those of Biondi. He described two sorts of cells in 
 the gland which he designated, respectively, principal cells, and 
 colloid cells. The principal cells constituted the main mass of 
 the epithelium. They were cylindrical or columnar cells, of 
 variable height in different species and in different ages of the 
 same animal species. They possessed a reticular protoplasm, 
 with granules at the nodal points, and an oval or round nucleus 
 situated at the basal end of the cell. Like Biondi he saw occa- 
 sionally in these cells small hyaline spherules, but considered 
 them to occur very rarely. The colloid cells differed from the 
 principal cells by the hyaline, transparent appearance of their 
 cytoplasm. This cytoplasm browned with osmic acid, and, in 
 dyes, stained the same as the colloid content of the follicles. 
 He found all grades of transition between the colloid cells and the 
 principal cells. He regarded the colloid cells as elements en- 
 gaged in the secretion of colloid but did not commit himself 
 definitely to the opinion that, after a period of secretion, they 
 might return to the state of the principal cells. He was like- 
 wise in doubt whether they degenerated or not after secretion. 
 
 V. Wyss ('89) studied the effects on the thyroid gland pro- 
 duced by poisoning with pilocarpine. He found in cats and dogs 
 that the gland after pilocarpine was large, turgid, and filled 
 with blood, and that the cells were larger, the nuclei less appar- 
 ent. The free ends of the cells were prolonged into processes 
 which were continuous with the colloid mass, and between these 
 processes were brilliant spherules of apparently fluid nature. 
 
 Anderson ('94) confirmed V. Wyss' conclusions relative to the 
 effect of pilocarpine on the gland, and studied the structure of 
 the epithelial cells in young cats and rabbits at different periods 
 of time after injections of pilocarpine. He described, in the 
 
40 R. R. BENSLEY 
 
 earlier phases of pilocarpinisation, the appearance of clear drop- 
 lets in the cytoplasm, which collected at the free pole of the 
 cell, to be extruded in the form of small droplets into the cavity 
 of the vesicle. These, therefore, he regarded as the antece- 
 dents of the clear vacuoles of the margin of the colloid and on 
 account of their lack of affinity for dyes, designated chromo- 
 phobe secretion. A little later round, stainable droplets made 
 their appearance in the free pole of the cell, which likewise mi- 
 grated to the free border to be extruded into the lumen, consti- 
 tuting thus the chromophile secretion. He regarded the colloid 
 cells of Langendorff as cells destined to degenerate. Thus, 
 Anderson rejected the mode of secretion favored by Langendorff, 
 and introduced the conception of a polyvalent secretion. His re- 
 sults, in general, are in more accord with those of Biondi than 
 with those of Langendorff. 
 
 Htirthle ('94) in the same year studied the effects of reduc- 
 tion of thyroid tissue, and of bile retention, on the secretory proc- 
 esses of the gland. He found, as a result of each of these con- 
 ditions, a great increase in the number of cells containing colloid 
 spherules, which -he therefore interpreted as an evidence of accel- 
 erated activity of the gland. On the other hand he recognized the 
 occurrence of the Langendorff colloid cells to which he also 
 ascribed secretory significance, and which he considered capable 
 of transformation into principal cells. 
 
 Galeotti ('96) studied the thyroid glands of the turtle Emys 
 europaea, under normal conditions, and after the injection of 
 various products of metabolism. He described two sorts of secre- 
 tion antecedents: fuchsinophile granules of nuclear origin, pre- 
 viously undescribed, and droplets of colloid like those described 
 by Biondi, Anderson, and Hurthle. These two secretion ante- 
 cedents varied independently of one another under the experi- 
 mental conditions employed. 
 
 Following Galeotti a number of different observers using his 
 methods studied the thyroid gland under different experimental 
 and pathological conditions, confirming his results as to the 
 double character of the thyroid secretion and the independent 
 variation of the two sorts of secretion. Among these may[be 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 41 
 
 mentioned Tiberti, and Ciulla. The latter identifies the fuchsin- 
 ophile granulations of Galeotti with the chromophobe secretion 
 of Anderson, the plasmosomes with the chromophile secretion of 
 the same author. 
 
 Lobenhoffer ('09) studied human thyroid glands, both normal 
 and pathological, in material fixed in formol Mtiller, and stained 
 in anilin acid fuchsin. He found, in his preparations, the cells 
 containing in widely varying amounts spherical fuchsinophile 
 granules about the size of the granules of eosinophile leucocytes. 
 Sometimes these granules formed a narrow row along the margin 
 of the cell, and sometimes very small granules were found actu- 
 ally in the margin of the colloid. These granules he regarded as 
 the antecedents of the thyroid secretion, interpreting the vary- 
 ing contents as indicating different phases of secretory activity. 
 
 As a result of the work of these observers we have to consider 
 the following structures, in connection with the secretory ac- 
 tivity of the thyroid cells, as possible intracellular secretion 
 antecedents : 
 
 1. Spherules of colloid, described by all observers except 
 Lobenhoffer. 
 
 2. Vacuoles containing a colorless unstaining fluid substance 
 described by Anderson as chromophobe secretion, and inter- 
 preted by him as the antecedent of the content of the vacuoles 
 seen in the margin of the colloid. 
 
 3. Colloid occurring as a diffusely distributed substance in the 
 cytoplasm of the so-called colloid cells of Langendorff. 
 
 4. The fuchsinophile granules of Galeotti. 
 
 5. The fuchsinophile granules of Lobenhoffer. 
 
 Recent work by O. Schultze, and Mawas has helped to reduce 
 the number of supposed secretion antecedents in the preceding 
 list by demonstrating the presence in the thyroid epithelial cells 
 of numerous mitochondria, usually filamentous, and oriented in 
 the direction of the main axis of the cells. There seems to be 
 little doubt that the fuchsinophile granules of Lobenhoffer are in 
 reality mitochondria, rather imperfectly preserved. To this cate- 
 gory belong also in part at least the fuchsinophile granules of 
 Galeotti, Tiberti, and others. Possibly however, a part of these 
 
42 R. R. BENSLEY 
 
 granule's are of another nature, since I have shown that in hyper- 
 plastic glands of the opposum and in human glands from cases 
 of exophthalmic goiter, non-mitochondrial fuchsinophile granules 
 occur. These will require further discussion when the secretory 
 by-products are considered. 
 
 With the exception of Hurthle, Langendorff , and Schmidt, prac- 
 tically all observers agree that the colloid cells of Langendorff 
 are cells in the last stages of cytomorphosis. The perfect grada- 
 tion between these cells and the so-called principal cells on the 
 one hand and the obviously degenerating cells of the follicle on 
 the other hand leaves little doubt of their significance. The 
 changes in the nucleus, the disappearance of mitochondria, and, 
 in many cases, the visible disintegration of the cytoplasm, or 
 desquamation of the cell, all point to the correctness of this 
 conclusion. 
 
 Thus by elimination we arrive at the conclusion that the only 
 secretory antecedents thus far demonstrated in the thyroid epi- 
 thelial cells which may be considered to be normal products, are 
 the colloid globules of Biondi, and Hurthle, to which belong also 
 the chromophile granules of Anderson, and the so-called chromo- 
 phobe secretion of Anderson. It is necessary, therefore to exam- 
 ine in greater detail the occurrence of these products in the thy- 
 roid epithelial cells, with the object of determining whether they 
 are actually related to the formation of intrafollicular colloid, 
 whether they are sufficient to account for the physiological ac- 
 tivity of the gland, and what indications they afford of the rate 
 of formation of the intrafollicular colloid. 
 
 Hurthle found that, when the thyroid tissue was reduced by 
 the removal of the whole of one lobe and two-thirds of the other, 
 in many places in the gland the epithelial cells contained droplets 
 of substance which was sharply defined by its staining reaction 
 from the surrounding protoplasm, but agreed in all respects with 
 the colloid contained in the follicular lumina. Similar results 
 he obtained by ligating the common bile duct and the thoracic 
 duct simultaneously. In these glands also he found the lym- 
 phatic vessels much dilated and filled with strongly staining col- 
 loid substance without admixture of formed elements. He con- 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 43 
 
 sidered two possible explanations of this phenomenon, namely, 
 that it was due to lymphatic obstruction, and that it was due to 
 accelerated activity of the gland, and decided in favor of the latter 
 alternative because ligation of the thoracic duct alone produced no 
 such changes in the gland. 
 
 Langendorff (loc. cit.) on the other hand, while admitting the 
 occasional occurrence of colloid droplets in the cells, did not con- 
 sider them of much significance from the secretory standpoint 
 because of their extreme rarity. Anderson also saw them, not 
 in the normal cell, but as a result of prolonged pilocarpinisation 
 of the animal. Schmidt could find no effect on the structure 
 of the epithelial cells as a result of pilocarpine injections, and at- 
 tached more importance to the colloid cells as an indication of 
 secretory activity. Bensley ('14) on the contrary, in studying 
 the involution of the hyperplastic gland of the opossum pro- 
 duced by the administration of iodides, found that the cells of 
 the gland practically all contained globules of colloid, and that 
 they could be seen discharging it into the lumen, while colloid 
 cells were almost completely lacking. In this case the restoration 
 of the intrafollicular colloid was wholly by the formation of in- 
 tracellular globules which discharged into the lumen. The proc- 
 ess however was an extremely slow one; after seventeen days, 
 though practically every cell contained a globule of colloid, as 
 large as, or larger than the nucleus, there was little intrafollicular 
 colloid, and at the end of twenty-four days of daily administra- 
 tion of iodides the condition was but slightly advanced; intra- 
 cellular colloid remained about the same as in the preceding case 
 but the follicular colloid was somewhat increased. Recent ex- 
 periments on the hyperplastic glands of the opposum have amply 
 confirmed these results; iodine administered daily to the animal 
 with a hyperplastic gland produces a gradual involution marked 
 by the slow accumulation in the cells of colloid droplets, usually 
 a single drop to a cell, and the ultimate discharge of these into 
 the newly formed lumen. We may consider it proven therefore 
 that the production of colloid under certain special conditions is 
 by this method. 
 
44 R. R. BENSLEY 
 
 This conclusion raises the question whether the production of 
 colloid under normal conditions of functioning is by the same 
 method, and, if so, what are the implications of this fact from the 
 standpoint of secretory rate? 
 
 Hurthle claimed that the formation of colloid droplets in the 
 epithelial cells of the thyroid gland was one of the ways of for- 
 mation of colloid and that their presence was an indication of 
 accelerated thyroid activity. Langendorff pointed out that they 
 were extremely rare, and therefore could not have the secretory 
 importance claimed by Hurthle. That Langendorff's contention 
 in this respect is correct will readily be admitted. Indeed, one 
 may search complete series of sections of small thyroid glands, 
 and thousands of sections of larger ones without finding in them 
 a single droplet of intracellular colloid. In six thyroid glands of 
 man obtained at autopsies on executed criminals, and examined 
 by the writer, only one contained epithelial cells with colloid 
 droplets in them. In pathological glands from cases of exoph- 
 thalmic goiter, simple colloid goiter, and colloid adenoma, on the 
 other hand, they occurred with variable frequency. In the one 
 normal gland that contained them the colloid drops occurred with 
 great frequency. For the most part they were placed not at the 
 free margin of the cell, but deep in the protoplasm, often along- 
 side of the nucleus, and in many cases several drops formed a row 
 extending from this deeper location to the free border. In many 
 follicles, however, the colloid droplets occupied the tips of the 
 epithelial cells, and in others the colloid masses inside the follicle 
 could be seen to be made up of a cluster of small droplets, ap- 
 parently derived from different cells, which had failed to fuse 
 with one another inside of the follicle. This gland also con- 
 tained an unusual number of colloid cells of Langendorff. 
 
 The obvious participation of these intracellular colloid drop- 
 lets in the replenishment of the intrafollicular colloid, on the 
 one hand, and the slowness of this process demonstrated by expe- 
 riment, and the rarity of the occurrence of such droplets under 
 normal conditions, on the other hand, suggest the following pos- 
 sibilities, which, however, are not, as will appear more clearly 
 later, mutually exclusive: (1) the formation of colloid is an inter- 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 45 
 
 mittent function of the thyroid cells; (2) there are other, at pres- 
 ent unknown mechanisms for the formation of colloid, correlated 
 with droplet formation, but able to proceed without it; (3) the 
 secretion of colloid into the gland lumen is an accessory and not 
 the primary function of the epithelial cells of the gland. 
 
 For the reasons mentioned above, it is apparent that the for- 
 mation of colloid droplets in the cell, at least, is an intermittent 
 function. It is possible, however, that in addition to this mode 
 of formation of colloid there is a slow and continuous production 
 of colloid at the free margin of the cell unaccompanied by the 
 formation of visible secretion antecedents in the cytoplasm, and 
 it may be that this latter is the main method of production of 
 intrafollicular colloid, the droplet method representing some 
 upset of secretory equilibrium which results in the accumulation 
 of the product of secretion in the cell, instead of the lumen. 
 That this hypothetical upset is of the nature of an acceleration 
 of the secretory rate is, however, excluded by the fact that we 
 often see the droplet formation in the greatest abundance in 
 adenomata the stroma of which is in an advanced state of hyaline 
 degeneration, and in which, therefore, there can be no question of 
 accelerated secretion rate. Histologically considered such a con- 
 ception of the process of secretion in the thyroid gland must 
 remain hypothetical, since it is incapable of objective proof. 
 
 The third possibility, namely, that the secretion of colloid in- 
 to the gland lumen is an accessory and not the primary function 
 of the epithelial cells, though correlated intimately with this 
 primary function, would, if established, explain and include all 
 of the facts. Such a theory to be accepted, must account for the 
 irregular occurrence of droplets, for their formation in the inte- 
 rior of the cell rather than on either of the free surfaces, and 
 for their increase under iodin or thyreoglobulin administration, 
 and under the experimental conditions of Hurthle. It involves 
 the assumption of a more remote antecedent of the secretion than 
 the colloid droplets of Hurthle. 
 
 In my studies of the thyroid glands of various mammals, I 
 have been struck with the frequent occurrence, particularly in 
 the cat, dog and opposum, of vacuoles with unstainable con- 
 
46 R. R. BENSLEY 
 
 tents, rather irregular in shape, occurring in the base of the cell, 
 and with the frequent occurrence in the cells of hyperplastic 
 human glands from cases of true exophthalmic goiter of droplets 
 of material staining like colloid located similarly in the extreme 
 bases of the cell near the capillary net. Ferguson ('11), also, 
 has described the occasional occurrence in the thyroid gland of 
 elasmobranch fishes of cells presenting in their basal ends a 
 ragged and rodded appearance which he interprets as due to 
 secretion storage for direct export to the vascular channels. 
 
 A group of opossums kept under observation under various 
 experimental conditions during the past winter have furnished 
 material in which, by reason of the fact that these vacuolar sub- 
 stances in the cell were unusually increased in amount, it was 
 possible to study their variation and to develop a technique for 
 staining of their contents. One group of these animals was kept 
 for a period of three weeks on a dietary consisting of beef, bread 
 and fat, egg, bread and fat, or cheese ; bread and fat, just suffi- 
 cient to maintain constant weight. In another group the diet 
 was so regulated that with constant bread and fat content there 
 was a progressive increment of meat fed to the successive mem- 
 bers of the series. In all of the animals thus kept on a controlled 
 diet, the thyroid cells contained such basal vacuoles, and in two 
 of the animals of the second series, namely those which received, 
 respectively, twice and two and a half times the normal meat 
 ration, the material of this sort comprised fully half of the cell 
 contents. 
 
 The fixation of the material is of considerable importance in 
 the study of these vacuolar substances, because the contents 
 are so dilute that they may be precipitated in an invisible form 
 on the protoplasmic strands which wall the vacuoles. Formalin 
 zenker, however, was found to precipitate the contents in the form 
 of a thin gel sometimes filling completely the space of the vacu- 
 oles, sometimes containing small vacuoles from contraction in 
 fixation. Staining however was difficult, because the material 
 stained with the usual dyes in the same way as the protoplasm. 
 With Mallory's connective tissue stain, however, it could be seen 
 that the vacuoles had vaguely staining contents, but, since the 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 47 
 
 protoplasm also stained bluish after formalin zenker fixation, it 
 was difficult to define accurately the limits of the vacuoles, and 
 after fixation in ordinary Zenker's fluid the vacuoles did not 
 stain at all. Accordingly the indication was to find some stable 
 stain which would stain the protoplasm diffusely, and then to 
 stain the secretion a contrast color. For this puropse brasilin 
 in phosphotungstic acid solution was found to be effective. The 
 solution is prepared as follows: 
 
 Phosphotungstic acid 1.0 g. 
 
 Distilled water 100.0 cc. 
 
 Brasilin 0.05 g. 
 
 The brasilin is first dissolved in a small quantity of distilled 
 water by the aid of heat and added to the phosphotungstic acid 
 solution. Ripening may be accelerated by the addition of 0.4 
 cc. of hydrogen peroxide, or of a few drops of a solution of soluble 
 molbydic acid. The solution deteriorates with age and should 
 not be used after three days. 
 
 Sections of thyroid glands which have been fixed in formalin 
 zenker, fastened to slides by the water method (if albumen is 
 used it should be very small in amount) are passed through 
 toluol, absolute alcohol, to water, iodised, and placed in the 
 staining solution from one to several hours. The sections are 
 then washed in water and placed for one to five minutes in the 
 following solution: 
 
 Phosphomolybdic acid 1.0 g. 
 
 Wasserblau 0.2 g. 
 
 Water 100.0 cc. 
 
 Then wash rapidly in water, dehydrate in absolute alcohol, clear 
 in toluol, and mount in balsam. 
 
 In the preparations so stained with brasilin and wasserblau 
 the cytoplasm stains pink to lilac, the nuclear chromatin, deep 
 red, and the contents of the vacuoles sky blue, as shown in Fig. 
 1. The colloid droplets of Hiirthle stain deep blue or deep red 
 according to the concentration of the gel which composes them, 
 which determines the diffusion rate of the dyes employed. 
 
48 R. R. BENSLEY 
 
 It must not be supposed that the technical difficulties of study- 
 ing tftis intracellular product are wholly overcome by the 
 method just described. When the material is large in amount 
 the method is very satisfactory, but the intensity of the proto- 
 plasmic staining is not sufficient to define the material sharply 
 when it is small in amount. Under these circumstances, a brief 
 mordanting of the section, before staining, in a fresh solution of 
 ammonium stannic chloride will improve the contrast staining, 
 but will detract greatly from the transparency and beauty of the 
 preparation. 
 
 The examination of the sections of the experimental series re- 
 ferred to above, and of a number of normal glands from animals 
 killed as soon as obtained, reveals the presence in all, although 
 in highly variable amounts in the individual members of the 
 series, of a new secretion antecedent. This substance is in the 
 form of vacuoles, occurring exclusively in the outer pole of the 
 cell, which contain a dilute solution similar in its properties to the 
 colloid of the follicular lumen, differing from the latter only in 
 density. There are even in this substance clear vacuoles due to 
 shrinkage in fixation, like those seen in the colloid of the lumen. 
 
 In two members of the experimental series, this substance is 
 present in such amount that it fills quite half the cell. In these 
 cases the cell presents an appearance comparable to that of the 
 secreting cells of an exocrine gland like the pancreas, with the 
 exception that the hylogens are in dilute solution in fairly large 
 vacuoles instead of in the form of granules, and they are in the 
 basal end of the cell instead of the free end. In other words 
 these cells exhibit the ordinary picture of a secreting cell with 
 stored secretion antecedents, but with reversed polarity. 
 
 Figure 1 shows an acinus from one of these glands. The cells 
 are cylindrical in shape with a spherical nucleus placed rather 
 nearer to the free end of the cell than to the base. The base of 
 the cell is filled with sky-blue stained material contained in 
 vacuoles separated from one another by thin sheets of cytoplasm 
 containing mitochondrial filaments. The free pole of the cell 
 directed towards the lumen is finely granular and stained a 
 bluish-pink color. It contains none of the blue staining vacuolar 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 49 
 
 material, and consists solely of cytoplasm containing crowded 
 rmtochondrial filaments. In two cells of this figure small glob- 
 ules of colloid may be seen, in one case alongside of the nucleus, 
 and in another in the apical cytoplasm. 
 
 In some of the thyroid glands obtained from opossums recently 
 captured, consisting of fairly large follicles well filled with col- 
 loid, the epithelial cells appeared uniformly vacuolated, but when 
 the preparations were stained with.brasilin and wasserblau the 
 vacuoles in the outer ends of the cells were found to be filled with 
 blue staining material, those in the inner ends with unstainable 
 material. 
 
 Three possible interpretations of the presence of this material 
 suggest themselves: first, that it is a pathological product rep- 
 resenting cytoplasmic degeneration, or imbibed serous fluid, or 
 simple edema; second; that it is colloid in process of resorption 
 by a transcellular route; third, that it is a true secretion ante- 
 cedent representing material formed in the base of the cell for 
 the purpose of direct transport into the vascular channels. 
 
 The fact that every cell of the gland contains the material, 
 that it is present in some degree in all opossum thyroid glands, 
 and that there are no other evidences of degeneration, such as 
 changes in the nucleus or in the mitochondria, or in the intra- 
 lobular connective tissue excludes the first possibility from con- 
 sideration. 
 
 Opposed to the second of these hypotheses is the fact that 
 only very exceptionally is this material found in the pole of 
 the cell in contact with the follicular content, and then only when 
 the cell is so loaded with the secretion that it is comparable in 
 appearance to a parotid gland cell filled with zymogen granules. 
 It might be possible to assume that the droplets of colloid occa- 
 sionally seen in the cell are on the way out rather than proceeding 
 towards the lumen. The evidence from the glands which are be- 
 ing reverted by iodine is, however, strictly opposed to this hy- 
 pothesis, since a progressive increase in colloid in these cases has 
 been demonstrated in an experimental series taken at different 
 intervals of time and this increase is associated directly with 
 colloid droplet formation and extrusion into the lumen. It is 
 
50 R. R. BENSLEY 
 
 conceivable, of course that the droplets of colloid are of two sorts, 
 those destined for the follicular content, and those on their way 
 to the base of the cell for secretion into the vascular channels of 
 the gland. Opposed to this assumption is the fact that in entire 
 glands, in the cells of which there is an abundance of the basal 
 vacuolar substance there may be found not a single droplet of 
 colloid of the dense type, and that the free poles of all the 
 cells may be wholly free from products of secretion except where 
 the crystals, of protein nature, demonstrated in a former article, 
 project into this pole. Furthermore, in hyperplasia of long 
 standing, in which there is practically no intrafollicular colloid, 
 a large content of the new secretion in the form of small vacuoles 
 distributed throughout the outer pole of the cell, may be present. 
 
 We are therefore forced to accept the third hypothesis which, 
 physiologically considered, is the more attractive, inasmuch as it 
 permits of harmonizing the various facts under a single hypothe- 
 sis, namely that the secretion collected in the outer pole of the 
 thyroid cell is destined to direct transport into the vascular chan- 
 nels, and that the thyroid cell represents a true reversal of 
 polarity in accord with its endocrine function. 
 
 In addition to the facts mentioned above which point strongly 
 to the correctness of this hypothesis, it may be pointed out 
 that in exocrine glands fat droplets which are deposited in the 
 secreting cells practically always make their appearance at the 
 anti-secretory pole of the cell; this is the case in the pancreatic 
 cells and in the chief cells of the gastric glands. The location 
 of the fat deposits in the thyroid gland also is at the pole which 
 according to the hypothesis here supported is the anti-secre- 
 tory pole of the cell, namely the free end of the cell next the 
 colloid. 
 
 We may assume therefore that the thyroid gland as all physio- 
 logical and clinical experience indicates, prepares and secretes 
 into the vascular channels of the gland a secretion, and that this 
 secretion is formed in the outer pole of the cell, and excreted from 
 it directly under normal conditions of functioning without passing 
 by the indirect route through the follicular cavity. 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 51 
 
 It is necessary, however, under this hypothesis to explain the 
 occurrence of intrafollicular colloid, and its variability in differ- 
 ent members of a species and under different experimental con- 
 ditions. In my recent studies on the changes in the hyperplastic 
 gland of the opossum and its changes under domestication, I have 
 shown that all the scored colloid may be withdrawn from the 
 gland in a short period, and that the gland will maintain for a 
 period of several months a condition in which little visible colloid 
 is present in the gland, but, as Marine previously demonstrated 
 in the dog, if iodine be administered the vesicles are reformed , and 
 filled with dense colloid. In the opossum this colloid makes its 
 appearance first deep in the thyroid cells, but migrates to the 
 free surface and is there discharged into the lumen. I have also 
 found in the study of many glands from cases of Basedow's dis- 
 ease that the few colloid droplets which are present are very fre- 
 quently found at the level of the nucleus, or even in the base of 
 the cell. These facts indicate that in addition to the direct 
 mode of secretion there is an indirect mode, which consists in the 
 condensation of the secretion into the form of droplets having a 
 high content of solids, and the extrusion of these droplets into the 
 follicular cavity. These droplets are formed in the same zone of 
 the cell as that in which the primary or direct secretion is formed, 
 and it is probable that they are formed at the expense of the 
 latter. 
 
 The readiness with which the thyroid gland undergoes hyper- 
 plastic change, its responsiveness to iodine administration, as 
 demonstrated by Marine and his co-workers, the ease by which 
 it may be modified structurally by dietary conditions as shown by 
 the work of Reid Hunt ('11), Marine, Chalmers Watson ('07), 
 Tanberg ('00), and Missiroli ('10) and confirmed by my recent 
 studies on the relation of diet to hyperplasia in opossums under 
 domestication, confirm the conclusion that there is a delicate ad- 
 justment between the functioning of the thyroid gland and general 
 body conditions, though at present we do not know the means 
 by which this adjustment is mediated. This being the case it 
 may be assumed that only when this adjustment is disturbed so 
 that the rate of secretion is in excess of body needs, the indirect 
 
52 R. R. BENSLEY 
 
 mode of secretion comes in, and the product of secretion is con- 
 densed and stored in the intrafollicular cavity. It is conceiv- 
 able, of course, that other factors than excess of production over 
 functional needs might bring about this result, as, for example, 
 an agent inhibiting direct export from the cell, or mechanical in- 
 terference with the outflow from the cells, The latter influence 
 is well illustrated in the colloid adenomata where, notwithstanding 
 the fact that the stroma may be hyaline, the cells contain abun- 
 dant colloid spherules, and thus give, according to the old criterion 
 of Hiirthle, the impression of high secretory activity. According 
 to my hypothesis of thyroid secretion, this condition would rep- 
 resent a slow secretory activity of the epithelium of the tumor, 
 all of the energy of which is, however, devoted to storage, since 
 direct export by way of the vascular channels is impossible. 
 This may explain the difference noted by Marine between the 
 hyperplastic gland and the adenoma as to susceptibility to influ- 
 ence by iodine. The hyperplastic gland, whether its activity be 
 high or low, is exporting its product directly. Iodine whether 
 by accelerating the activity of the gland and so producing a con- 
 dition of physiological saturation with thyroid products, or by 
 actually inhibiting the export of material from the cell, causes the 
 cell to reverse its processes, and store it in the follicular cavities. 
 The adenoma is already storing all of the product which the 
 vascular conditions and its specific cell equilibrium permit it to 
 form, and so the process can not be influenced by iodine. 
 
 According to this conception of thyroid secretion the colloid 
 in the thyroid vesicles is per se no measure of the activity of 
 the gland at the moment of observation, though its consistence 
 and its qualities may offer valuable indications of the capacity 
 of the thyroid cell for normal storage. The colloid in fact may 
 be the product of a storage phase which preceded the exafnina- 
 tion of the gland by a considerable period of time, since it is 
 necessary to assume the resorption of this material only under the 
 conditions where the normal direct secretory activity of the, gland 
 is insufficient to meet the functional demands. Accordingly, 
 also, lack of colloid in the gland does not necessarily mean de- 
 pression of the gland activity below the normal rate at the time 
 of observation, though it probably does mean that there is such a 
 
N T ORMAL MODE OF SECRETION IN THYROID GLAND 53 
 
 depression of physiological efficiency or has been at some pre- 
 vious time, and either that the gland has not risen above the 
 level of secretory rate needed for direct export, or that there has 
 been a failure of the normal mechanism of regulation. My ob- 
 servations on the hyperplastic glands of opossums by means 
 of the methods described in this paper have shown that hyper- 
 plastic glands which appear almost identical histologically may 
 yet differ markedly in the amount of these intracellular secre- 
 tion antecedents which they contain, and thus, probably, in 
 secretory potential. 
 
 BIBLIOGRAPHY 
 
 ANDERSSON, O. A. 1894 Zur Kenntniss der Morphologie der Schilddriise. Arch 
 
 f Anat. u. Entwcklngs., Anat. Abth., Leipzig, pp. 177-224. 
 BEXSLEY, R. R. 1914 The thyroid gland of the opossum. Anat. Record, 8, pp. 
 
 431-440. 
 BIONDI, D. 1892 Contribution a 1'etude de la Glande Thyroide. Revue, Arch. 
 
 ital. de biol., Par., xvii, pp. 475-77 
 CIULLA, M 1910 Gli organi a secrezione interna nella gravidanza e nel puer- 
 
 peno Ginecol. Moderna. 
 FERGUSON, .1. S. 1911 The anatomy of the thyroid gland of elasmobranchs, 
 
 etc. Am. Jour. Anat., 11, pp. 151-209. 
 GALEOTTI, G. 1897 Beitrag zur Kenntniss der Sekretionserscheinungen in den 
 
 Epithelzellen der Schilddriise. Arch. f. mikr. Anat., Bonn, 48, pp. 
 
 305-28. 
 HUNT, REID 1911 Experiments on the relation of thyroid to diet. J. Am. 
 
 Med. Ass., Chicago, 57, pp. 1032-33. 
 HURTHLE, K. 1894 Beitrage zur Kenntniss des Secretionsvorgangs in der 
 
 Schilddriise. Arch. f. d. ges. Physiol., Bonn, Ivi, pp. 1-44. 
 LANGENDORFF, O. 1889 Beitrage zur Kenntniss der Schilddriise. Arch. f. 
 
 Anat. u. Physiol., Physiol. Abth., Supp., pp. 219-42. 
 LOBENHOFER, DR. 1909 Beitrage zur Lehre der Sekretion in der Struma. 
 
 Mitth. a. d. Grenzgebieten d. Med. u. d. Chir., Jena, 20, pp. 650-62. 
 MARINE, D. 1914 The rapidity of the involution of active thyroid hyperpla- 
 
 sias of brook trout following the use of fresh sea fish as food. J. Exp. 
 
 Med., N. Y., 19, pp. 376-82. 
 
 TANBERG A., AND MISSOROLI, A. 1913 Quoted after Biedl, A. Innere Sekre- 
 tion, Zweite Auflage, Berlin u. Wien, Urban u. Schwarzenburg. 
 TIBRRTI, N. S. 1905 Sulla attivita secretoria della ghiandola tiroide in alcuni 
 
 condizione morbose. Lo Sperimentale, 59. 
 WATSON. C. 1907 On changes in the structure of the thyroid gland in wild rats 
 
 under the influence of altered dietetic conditions. Proc. Physiol. 
 
 Soc., Lond. May 18, pp. 1-3. 
 
 WYSS, R. v. 1889 Ueber die Bedeutung der Schilddriise. Korresp. f. Schweit- 
 zer Aertzte, 19. 
 
 THK AMERICAN JOURNAL OF ANATOMY, VOL. 19, NO. 1 
 
54 R. R. BENSLEY 
 
 EXPLANATION OF PLATE 
 
 1 A group of follicles from the thyroid gland of the opossum, fixed in forma- 
 lin zenker, stained with brasilin-wasserblau. X 1050. In the outer poles of the 
 cells a material differentially stained, similar to the intrafollicular colloid. In 
 two cells droplets of colloid destined for storage. 
 
NORMAL MODE OF SECRETION IN THYROID GLAND 
 
 R. R. BEN8LBY 
 
 PLATE 1 
 

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