It may not be amiss to observe, after this review, that the disease of the thyroid, which is of by far the most frequent occurrence, viz. enlargement of its magnitude from excessive or perverted secretory action, is just of the kind we should, from our knowledge of its actual structure, expect would be most liable to occur. For when once the nicely arranged balance of secretion and absorption, with its moderate alternating oscillations in either direction, is permanently deranged, the closed cavities of the glandular vesicles afford no exit to the accumulating matters. Thus does minute anatomy explain, and thus is it con firmed by, the changes wrought by disease.
HisTony OF INVESTIGATIONS. - The fol lowing is not presented as a complete history of the thyroid, but as a sketch which it is hoped contains the principal facts relative to the advance of our knowledge respecting it.
In examining the works of Aristotle, I find he makes no mention of the thyroid in two places, where he describes the organs situated in the neck, and speaks especially of the trachea. Galen does not give any very dis tinct account of the thyroid, so far as I have been able to discover ; but certainly seems to allude to it in a passage in his book " On the Use of the Parts of the Human Body," where he speaks of the glands of the larynx, " which are always found more loose and spongy than others, and which, by the common consent of anatomists have been created for the purpose of moistening and bathing all the parts of the larynx and the passage of the throat." The following passage, quoted also in a note by Morgagni*, seems to prove that he was aware of the main peculiarity of the thyroid. " Now the neck has two glands, in which a moisture is generated. But from the two glands which are in the neck there come forth no vessels by which the moisture may flow out, as those do from the glands of the tongue." Vesalius, who wrote about A.D. 1542, dis tinctly recognises the existence of the thyroid in the following passage from his work, " De corporis humani fabrich." t "And this dissec tion also shows two glands, adhering one on each side, to the root of the larynx, which are of large size, and very fungous, and nearly of the colour of flesh, but darker, and covered over with very conspicuous vessels." In the second book he describes their appearance in oxen, in whom they resemble muscular tissue, he says, very much, while in man their aspect is more truly glandular. Jacobus Sylvius, who wrote
a little later than Vesalius, enumerates, in his list of glands, "dum item ad laryngis radicem aspermque arterim initium utrinque una qum mterduin ob magnitudinem in unam shire videntur." Wharton, in his Adenographia, published about 1656, gives a very full and good description of the thyroid ; he notices its situation, figure, magnitude, texture (sub stantiam), and consistence (soliditatem) ; and remarks " that it is much more full of blood than any other gland, also more viscid and solid, and more resembling muscular flesh. This is the only difference, that it is not of a fibrous structure, but rather of a glutinous nature." He assigns four uses to the gland, which it may be worth while to quote, as affording an example of the speculations then in vogue, the last perhaps being not the least real and important of those he mentions ! " (1) The first and principal use of these glands appears to be to take up certain superfluous moistures from the recurrent nerve, and to bring them back again into the vascular system by their own lymph channels. (2) To cherish the cartilages to which it is fixed, which are rather of a chilly nature, by its own heat ; for it is copiously supplied with arteries, and abounds with blood, from whence it may conveniently impart heat to the neighbouring parts. (3) To conduce by its exhalations to the lubri cation of the larynx, and so to render the voice smoother, more melodious, and sweeter. (4) To contribute much to the rounded con tour and beauty of the neck ; for they fill up the empty spaces about the larynx, and make its protuberant parts almost to subside and become smooth, especially in the female sex, to whom on this account a larger gland has been assigned, which renders their necks more even and beautiful." Verheyen, writing about 1720, describes the thyroid as deriving its name from the cartilage so called, and states that it is con sidered by some as double, i. e. consisting of two glands. He says, "this gland, beyond doubt, serves also to moisten the neighbour ing parts ; but, because it is very large, there is an apparent reason why it should have rather large excretory ducts, or one at least very conspicuous, which yet hitherto has not been discovered." About 1708, Evertzen wrote an inaugural dissertation on the thyroid gland, noticing its structure, some diseases to which it is liable, and their treatment.