TH YROID S AND PA RA TH YROID S 



635 



great interest, because of the careful manner in which it has been 

 studied, is the endemic goitre (sometimes erroneously termed ' car- 

 cinoma ') of brook trout kept under artificial conditions in 

 hatcheries. Marine has shown that this depends upon overfeeding 

 with unsuitable food (such as livers of cattle, pigs, or sheep), over- 

 crowding, and insufficiency of water-supply, and that the goitre 

 can be readily cured or prevented by changing the conditions in 

 these respects. Similar results have been obtained in mammals fed 

 exclusively with meat. Thus, lion cubs at the Zoological Gardens 

 in London on a diet consisting only of raw meat developed rickets 

 and goitre, as did puppies fed with meat, lungs, liver, or heart, and 

 nothing else; whereas when milk, bread, and bone were added to 

 meat the puppies grew nor- 

 mally (Marine). A meat diet 

 caused hyperplasia of the 

 .thyroid in rats (Chalmers 

 Watson). The relation of the 

 disease known as exophthal- 

 mic goitre to the thyroid 

 has been much debated. The 

 best evidence is against the 

 hypothesis that the symp- 

 toms are due to increased 

 activity of the thyroid func- 

 tion (so-called hyperthyroid- 

 ism). All attempts to pro- 

 duce anything resembling 

 the pathological condition by 

 the administration of large Fig - 2 3 ' -Microphotograph of Active Thyroid 



amounts of thyroid or of 



thyroid products have failed. 



Nor has it ever been shown 



that the changes in the gland 



are the primary cause of the 



syndrome. Indeed, no specific anatomical or chemical changes 



have as yet been demonstrated in the thyroid in this condition. 



The thyroid gland of exophthalmic goitre has the same action on 



animals and on patients suffering from exophthalmic goitre as any 



other thyroid gland with like iodine content (Marine). 



The relations of iodine to the gland itself, and the modifications 

 in its structure and function determined by the giving or withholding 

 of iodine, recently studied by Marine, are of great interest, fin all 

 animals, so far as examined, the normal thyroid contains iodine. 

 The amount is variable) but the minimum percentage of iodine 

 necessary, if the normal nistological structure is to be maintained, 

 is quite constant for a given species. So also the highest percentage 



Hyperplasia from a Case of Exophthalmic 

 Goitre (Marine). The characteristic changes 

 in the hyperplastic gland the infoldings 

 and plications of the alveolar epithelium, 

 the great reduction in the colloid, and the 

 increase in the Strom a are shown. 



