650 



INTERNAL SECRETION ENDOCRINE GLANDS 



Thus, lion cubs at the Zoological Gardens in London on a diet con- 

 sisting 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 

 exophthalmic goitre to the thyroid has been much debated. The 

 best evidence is against the hypothesis that the symptom complex 

 is of thyroid origin. The increased thyroid activity partially 

 accounts for the increased metabolism characteristic of the disease ; 

 but this is secondary and symptomatic. All attempts to produce 



anything resembling the 

 pathological condition by 

 the administration of large 

 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 ex- 

 ophthalmic 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. In all animals, so far as examined, the normal thyroid 

 contains iodine. The amount is variable, but the minimum per- 

 centage of iodine necessary, if the normal histological structure is 

 to be maintained, is quite constant for a given species. So also the 

 highest percentage of iodine associated with any degree of active 

 hyperplasia (developing goitre) is always below the normal minimum 

 of oi per cent, of the dried gland as shown by Marine in the dog, 

 sheep, man, and other mammals. As active hyperplasia of the 

 thyroid (goitre) (Fig. 203) develops, the iodine content of the gland, 

 both relative and absolute, decreases, until in extreme degrees of 

 the condition there may be no demonstrable iodine present at all. 



Fig. 203. Microphotograph of Active Thyroid 

 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 stroma are shown. 



