INTERNAL SECRETIONS 



517 



Cretins and cases of myxoedema show marked improvement when 

 fed upon thyroid gland. It was noticed that a condition " cachexia 

 thjTeopriva " similar to myxoedema was induced when the goitrous 

 thyroid was removed by operation ; hence it became customary always, 

 to leave a piece of thyroid tissue. 



In contrast to the condition due to lack of thyroid activity is that 

 known as i- exophthalmic goitre," or "Graves' disease" (Fig. 255). 

 In this disease the thyroid is generally enlarged and overactive. 

 This "overaction " manifests itself in "nervous " symptoms exoph- 

 thalmos and tachycardia. On account of the nervous symptoms, 



FIG. 254. TYPICAL CASE OF MYXCEDEMA. (Photographs kindly lent by Dr. 

 Robert Hutchison.) 



A, Before treatment; B, after treatment. 



the disease has been regarded by some as primarily a lesion of the 

 sympathetic nervous system, and not of the thyroid gland. A 

 possible explanation of this may be that mam 7 of the symptoms 

 are due to the increased action of adrenalin upon sympathetic nerve 

 endings, this increase being due to the excessive thyroid secretion 

 (cf. p. 519). 



The results of extirpation experiments, on the whole, support 

 clinical observation. There is, however, much contradiction in the 

 evidence, owing to the fact that extirpation of the thyroid and of the 

 parathyroids produces different effects in different species of animal. 

 It is difficult to produce all the symptoms of myxoedema as a result 

 of thyroid deficiency; possibly, therefore, some other factors come into 



