1 54 



THE THYROID. 



septa into lobules, the lobules being separated by fine intra-lobular lamellae of connective-tissue- 

 into follicles (0*5-1 "5 mm.)- These follicles make up the gland-substance, and they are usually 

 polygonal when seen in a section. Each follicle consists of a cortical and a medullary part, 

 and the matrix or framework of both consists of a fine adenoid reticulum whose meshes are 

 filled with lymph -corpuscles " (fig. 126, a).] Many of these corpuscles exhibit various stages 

 of disintegration. In the medulla are found the concentric corpuscles of Hassall. ["They 

 consist of a central granular part, around which are disposed layers of flattened nucleated 

 endothelial cells arranged concentrically. When seen in a section they resemble the 'cell- 

 nests' of epithelioma (tig. 126, b). They have also been compared to similar bodies which 

 occur in the prostate. They are most numerous when the gland undergoes its retrograde 

 metamorphosis." Sig. Mayer finds that the thymus of the frog contains structures, with 

 transverse markings, identical with the stripes of striped muscular fibres. The structures are 

 identical with those called " sarcoplasts " by Margo and Paneth, and " sarcolytes " by Sig. 

 Mayer. They also occur in large numbers in the tail of the larvae of batrachians, when the tail 

 is undergoing a retrograde metamorphosis.] 



Simon, His, and others described a convoluted blind canal, the "central canal," as occur- 

 ring within the gland, and on it the follicles were said to be placed. Other observers, 

 Jendrassik and Klein, either deny its existence or regard it merely as a lymphatic or an 

 artificial product. Numerous fine lymphatics penetrate into the interior of the organ, and 

 many are distributed over its surface, but their mode of origin is unknown. [They seem to be 

 channels through which the lymph-corpuscles are conveyed away from the gland.] Numerous 

 blood-vessels are also distributed to the septa and follicles (fig. 125, c). 



Chemical Composition. Besides gelatin, albumin, soda-albumin, there are sugar and fat, 

 leucin, xanthin, hypoxanthin, formic, acetic, butyric, and succinic acids. Potash and 

 phosphoric acid are more abundant in the ash than soda, calcium, magnesium (? ammonium), 

 chlorine, and sulphuric acid. 



Function. As long as it exists, it seems to perform the functions of a true lymph-gland. 

 This view is supported by the fact that in reptiles and amphibians, which do not possess 

 lymph-glands, the thymus remains as a permanently active organ. [Extirpation gave few positive 

 results, but chemical investigation shows that the parenchyma contains a large number of 

 products indicating considerable metabolic activity (Friedleben).] 



in. The Thyroid. Structure. The gland consists of lobes and lobules held together by 

 connective-tissue rich in cells. Each lobule is made up of numerous completely closed sacs 



(0'04 toO'l mm. in diameter), which 

 in the embryo and the newly -born 

 animal are composed of a membrana 

 propria lined by a single layer of 

 nucleated cubical cells (fig. 127). 

 The sacs contain a transparent, viscid, 

 albuminous fluid. [Not unfrequently 

 the sacs contain many coloured blood - 

 corpuscles (Baber). ] Each sac is sur- 

 rounded by a plexus of capillaries 

 which do not penetrate the mem- 

 brana propria. There are also numer- 

 ous lymphatics. At an early period 

 the sacs dilate, their cellular lining 

 atrophies, and their contents undergo 

 colloid degeneration. When the 

 gland-vesicles are greatly enlarged, 

 " goitre " is produced. 



The chemical composition of this 

 gland has not been much investigated. 

 In addition to the ordinary constitu- 

 ents, leucin, xanthin, sarkin, lactic, 

 succinic, and volatile fatty acids have 

 been found. 



[Excision. The effects differ ac- 

 cording to the animal operated on. 

 This gland has been excised in the human subject in cases of goitre. Reverdin pointed out that 

 a peculiar condition results, called cachexia stumipriva, and practically the human being 

 becomes a cretin. This operation therefore is highly questionable when performed on man. 

 Babbits endure the operation well, and so do the sheep, calf, and horse. Of dogs, cats, and 

 foxes, only a very small number survive, nearly all die. It appears therefore that herbivora bear 

 the operation and suffer fewer after-effects than carnivora (Sanquirico and Orecchia). The 

 immediate effects are fibrillar contractions, which ultimately influence the gait of the animals, 

 convulsions, anaesthesia, great diminution of sensibility, loss of flesh, redness of the ears and 



Fig. 127. 

 Section of the thyroid gland, a, closed vesicles; b, dis- 

 tended by colloid masses and lined by low columnar 

 epithelium ; c, inter- vesicular connective-tissue. 



