442 MANUAL OF HISTOLOGY. 



From the peripheral network formed of canals burrowing through the 

 connecbive-t issue of the capsule, lateral ramifications are given off, which 

 penetrate into the interior, and gradually enclose the primary lobes in 

 complete rings, or more or less perfect arches (d, d). From these a few 

 fine terminal passages with blind ends (e) are seen sinking in between the 

 different vesicles. 



The nerves supplying this organ do not spring from the vagus or hypo- 

 glossus, but from the sympathetic, entering with the vessels of the part. 

 They consist for the most part of non-medullated fibres, forming trunks 

 with numerous branches, which ramify amid the connective -tissue 

 between the lobes and lobules. Among them may be seen ganglion cells, 

 partly isolated, and partly arranged in groups of from 2 to 5. Their 

 mode of termination is as yet unknown, except so far that fine terminal 

 filaments are lost in the connective-tissue bounding the vesicles. Con- 

 trary to the general opinion, the thyroid gland cannot be said to be poor 

 in nerves, nay, in the calf it appears even to be richly supplied with the 

 latter (Peremeschko). 



The structure, as it has just been described, undergoes, however, a rapid 

 change, even at an early period, so that in the infant, even, we may meet 

 over a considerable area with modified glandular tissue, in such quanti- 

 ties sometimes as to render the recognition of its original structure of 

 some difficulty. The glandular cavities now become more and more 

 filled with a homogeneous transparent and semifluid substance (fig. 425, 

 5, c), a product of ?he transformation of the gland cells to which the name 

 colloid matter has been given (fig. 426). Later on in life the cavities 

 just described undergo in the human being a great increase in volume 

 through increase of the colloid matters, and most unmistakably at the 

 expense of the interstitial connective- tissue, which suffers compression. 

 An extreme degree of colloid accumulation leads not unfrequently in man 

 to a considerable enlargement of the whole organ, constituting that con- 

 dition known as goitre, the glandular struma of Ecker. 



This progressive colloid metamorphosis, in which small whitish semi- 

 transparent points may be seen even with the naked eye, gives rise to 

 compression of the interstitial connective-tissue, and with it of the 

 lymphatic canals embedded in it. In consequence of this the absorbent 

 apparatus decreases more and more in efficiency, while the blood-vessels, 

 which remain pervious for a longer time, continue to supply material for 

 a continuation of the colloid metamorphosis. Further accumulation of 

 this substance leads to obliteration of the gland vesicles, the connective- 

 tissue disappearing, and the cavities opening into one another. If we 

 now examine a portion of the gland in which the process has advanced 

 to this stage, each lobe appears as a pale yellow coloured jelly-like mass, 

 enveloped in a network formed of the dwindling and half-macerated con- 

 nective-tissue bundles. Finally, it may come to pass that a whole lobe is 

 metamorphosed into a pellet of colloid matter. Hand and hand with these 

 changes anatomical transformations take place in the gland cells, the 

 latter becoming filled with the same substance, and finally undergo 

 solution. 



The views regarding the functions of the thyroid gland are still only 

 hypothetical. The fluid which may be pressed out of its substance con- 

 tains leucin, hypoxanthin, as well as volatile fatty acid, and lactic and 

 succinic acids. The specific gravity of the organ has been set down by 

 Krause and Fischer at 1 '045. 



