764 THE THYROID BODY. [BOOK n. 



such a provisional supposition than to conclude that the thyroid 

 may be removed without producing any effect whatever on the 

 organism. An animal without a thyroid may appear perfectly well 

 because the circumstances to which it is exposed do not happen to 

 test the imperfection from which it is really suffering, just as a 

 man's inability to swim may not be apparent until he happen to fall 

 into the water. The animals which do succumb to the operation of 

 removal of the organ are, for some reason or other, put to the test, 

 and are found wanting. The very discordance of the experimental 

 results points the physiological moral that the phenomena which 

 we are as yet able to observe form as it were a mere surface 

 covering intricate processes at present wholly or nearly wholly 

 hidden from us. 



The above experimental results receive additional interest and 

 at the same time support from clinical experience. The connection 

 between goitre and civtinism, the latter disease being broadly 

 speaking a result of disordered nutrition telling largely on the 

 nervous system, has long been recognised ; and attention has also 

 been called to some tie between disease of the thyroid and a morbid 

 condition, known as myxoedema, in a certain number of cases of 

 which mucin or a mucin-like body has been found in great excess 

 in the skin and in other tissues. In monkeys the removal of the 

 thyroid has, in some cases, been followed, besides the symptoms 

 mentioned above, some of which resemble those of myxcedema, by 

 an accumulation of mucin or a mucin-like body in the skin and 

 various tissues. It is very difficult not to connect this with the 

 formation in the thyroid of colloid material in the contents of the 

 alveoli. But we know so little about the nature of mucin and 

 its allies, about their real relations to more ordinary proteid sub- 

 stances, and about the part which they play in physiological pro- 

 cesses, that any views as to the exact connection between the 

 presence of mucin in the tissues at large and changes taking 

 place in the thyroid must be at present to a large extent 

 speculation. 



The large vascular supply of the thyroid, and the phenomena 

 of a disease known as exophthalmic goitre, in which vascular en- 

 largement of the thyroid is associated with cardiac symptoms and 

 other vascular disturbances, especially of the head, have suggested 

 that, apart from metabolic processes, the circulation in the thyroid 

 may, perhaps in a more or less mechanical way, be connected with 

 and influence the circulation in the brain. But the exact nature 

 of this influence has not been made clear. 



496. The Pituitary Body. The lower, posterior, lobe of 

 this organ resembles the thyroid body (the upper, anterior, lobe is 

 of quite distinct nature, being really a part of the central nervous 

 system) in as much as it is a diverticulum of the alimentary canal 

 (namely of the mouth), which instead of becoming a branched 

 gland is converted into a mass of round, or oval, or cylindrical 



