THYROID GLAND. 



1113 



the absorbent glands, which doubtless produce 

 some change in the fluid which traverses them ; 

 this, however, must necessarily be a rapid 

 process, and, accordingly, scarce any cells are 

 formed ; the mass of the glandular paren- 

 chyma consisting of very perfect nuclei; (2), 

 the terminal hepatic ducts, whose walls, as I 

 have shown, consist almost entirely of nuclei 

 set close together, and which, by means of 

 these effective agents, eliminate the actual 

 biliary secretion from the varying, partly 

 biliary, partly oily, fluid formed by the hepatic 

 cells on their exterior ; this process of elimi- 

 nation is, I believe, continually going on, and 

 is not so much of a metabolic as of an ab- 

 sorbing nature; the essential change being 

 probably effected by the hepatic cells of the 

 lobules; (3) the nucleated tissue forming the 

 principal part of the villi, which scarce ever 

 developes cells,* but is constantly attracting 

 the chylous fluid through the basement mem- 

 brane from the cavity of the gut, and permit- 

 ting it to pass off by the efferent lacteals 

 (here scarce any chemical change appears to 

 take place) ; (-t) the cineritious matter of the 

 cerebral hemispheres, which, amid the rapid 

 alternations of sensation, thought, and volition, 

 must be undergoing incessant change, consists, 

 in by far the greater part, of nuclei and granular 

 matter, the fully formed vesicles being few and 

 far between. 



Applying, now, these views to the case of 

 the thyroid, there seems reason to believe that 

 the ordinary condition of its epithelium is such 

 as to adapt it for rapid and transitory action ; 

 so that a large amount of secretion may be 

 quickly thrown into its cavities on any sudden 

 occasion ; which again would easily transude 

 through the thin epithelial layer and homo- 

 geneous tunic, when the time of action had 

 passed by. 



It may also be remarked, as consonant 

 with the views above stated, that as respects 

 its chemical nature the secretion of the thy- 

 roideal cavities is of a simple kind, not appa- 

 rently requiring much elaboration. It seems, 

 in fact, to be a mere modification of albuminous 

 matter containing, it may be, some gelatine, 

 but strongly contrasting with the highly 

 wrought products of the renal and hepatic 

 laboratories. This implies that the change 

 effected by the thyroideal epithelium on the 

 liquor sanguinis supplied to it is by no means 

 considerable. 



USE. Cruveilhier, writing about fifteen 

 years ago, briefly says, " the use of the secre- 

 tion of the thyroid is unknown ; " nor can 

 the anatomist of the present day give a 

 much more satisfactory account. So en- 

 veloped in mystery the use of the gland seems 

 to have been always regarded, that inquirers 

 have been more willing simply to confess 

 their ignorance than is usually the case, and 

 fewer speculations and hypotheses have been 

 broached respecting this than regarding other 

 points which promised at first sight to be of 

 easier solution. It is scarcely worth while 



* I venture herein to differ from Professor Good- 

 sir) not without repeated and careful observations. 



to mention the opinion, which supposes the 

 thyroid to have any essential connexion with 

 the larynx, either as pouring into it, through 

 supposed ducts, a fluid fitted to lubricate the 

 lining membrane, or, as Sir A. Carlisle sup- 

 posed, forming a protection to the delicate 

 organs of the voice, against the variations 

 in temperature of the external air. There 

 seems no doubt that the relative position of 

 the thyroid to the larynx is quite unimportant, 

 so far as the function of the organ is con- 

 cerned. This is borne out by the variations of 

 its site which occur in birds, and by the results 

 of morbid action ; since prodigious goitre does 

 not induce disease of the larynx, except in a 

 mechanical way, i. c. by injurious pressure. 



Passing over more crude conceptions, we 

 come to consider a theory which has been 

 propounded by Mr. Simon, and which has 

 certainly every claim to our careful attention, 

 both from the character of its author, and as 

 it is the only one yet promulgated which can 

 be said to be even probable. He considers 

 that the thyroid acts as a diverticulum to the 

 cerebral circulation ; exercising, at the same 

 time, its secretory function in an alternating 

 manner with the encephalic nervous mass. 

 His words are, " What diversion is to the 

 stream of blood viewed quantitatively, alter- 

 native secretion would be to the composition 

 of blood viewed qualitatively ; and I should 

 conceive that the use of the thyroid gland, in 

 its highest development, may depend on the 

 joint exercise of these two analogous func- 

 tions. I should suspect not only that the 

 thyroid receives, under certain circumstances, 

 a large share of the blood which would other- 

 wise have supplied the brain, but also that the 

 secretion of the former organ bears some 

 essential relation (which chemistry may here- 

 after elucidate) to the specific nutrition of the 

 latter ; that the gland, whether or not it 

 appropriates its elements in the same proxi- 

 mate combination as the brain does, may, at 

 all events, affect, in a precisely similar degree, 

 the chemical constitution of the blood tra- 

 versing it ; so that the respective contents of 

 the thyroid and cerebral veins would present 

 exactly similar alterations from the characters 

 of aortic blood. Finally, I should suppose 

 that these actions occur only, or chiefly, during 

 the quiescence of the brain, and that when 

 this organ resumes its activity the thyroid may 

 probably render up again from its vesicles to 

 the blood, in a still applicable form, those 

 materials which it had previously diverted 

 from their destination." 



This theory mainly rests on the circum- 

 stance that the thyroideal arteries arise in 

 close proximity to the cerebral, and this is 

 I think sufficiently constantly the case to form 

 a strong argument in its favour. It must be 

 remembered, however, that variations in the 

 place of origin of the arteries both of the brain 

 and thyroid, do occur without, as far as we 

 know, any interference with the full discharge 

 of the functions of the gland ; and it may also 

 be considered probable that the purpose of a 

 diverticular stream would have been better 



