CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 799 



a condition which itself seems to aggravate matters, since the 

 various symptoms are alleviated by artificial warmth and made 

 worse by exposure to cold. All these various symptoms, unless 

 remedial measures be taken, bring out in the end the death 

 of the animal operated on ; and in general the effects of the 

 removal are more marked and acute in young than in old 

 animals. 



These various characteristic effects of the operation are 

 undoubtedly due to the actual removal of the organ, and not 

 to mischief set up in adjoining structures, such for instance as 

 the vagus nerves. Moreover, as in the somewhat analogous case 

 of the pancreas ( 468), the whole organ must be completely 

 removed; if only a small part of the organ be left behind, or 

 if any 'accessory' thyroid be left, the symptoms do not make 

 their appearance. And again as in the case of the pancreas, 

 if a portion of the organ be transplanted and grafted, the whole of 

 the remaining thyroid may be removed without ill effects, but 

 these make their appearance so soon as the transplanted portion is 

 also removed. We seem justified in inferring that the thyroid 

 exercises some influence on the blood whereby the fitness of the 

 blood for the nutrition of the body is maintained. Whether that 

 influence is exerted by the thyroid doing away with or changing 

 some substance or substances brought to it in the blood, or by 

 its adding some substance or substances to the blood directly 

 or indirectly through the lymphatic system, we cannot at present 

 with certainty say. That the latter view is, however, the more 

 probable seems to be shewn by the fact that the ill effects of the 

 removal of the thyroid may be obviated by simply injecting 

 repeatedly into the body of the animal operated on a small 

 quantity of an aqueous extract of fresh thyroid. The addition to 

 the blood of some constituent or other present in the extract, 

 restores the nutrition which was failing. 



While in the animals above mentioned the ill effects of re- 

 moval of the thyroid are so striking, in other animals, for instance 

 herbivora, they are much less, or come on at a much later period, 

 or may be apparently wholly wanting. Why this is has not at 

 present been fully explained. 



Besides the above experimental evidence we also possess 

 clinical evidence almost equally striking. The disease in man 

 known as myxoedema, the symptoms of which are very similar to 

 those following removal of the thyroid in animals, being those of 

 disordered nutrition, especially of the skin (including at times an 

 apparent excess of mucin, though this is by no means constant, 

 and the name myxcedema unfitting), accompanied by nervous 

 troubles is closely associated with morbid changes in the thyroid 

 body. Moreover the dependence of the symptoms in question on 

 some failure in the work of the thyroid is shewn by the remark- 

 able amelioration or even almost disappearance of the symptoms 



