634 INTERNAL SECRETION 



theless, the consequences of complete removal of the thyroid proper 

 are in general more serious in the carnivora than in the herbivora. 

 [Muscular weakness soon becomes marked; the tissues waste, the 

 'temperature becomes subnormal, and this is associated with changes 

 in the heat regulation) (p. 673). If a portion of the thyroid be 

 left, or a graft be mad4 of some thyroid tissue from an animal of 

 the same species, these effects are entirely obviated so long as the 

 graft survives. It has not been established that a hetero-thyroid 

 graft i.e., a graft of thyroid tissue from an animal of a different 

 kind even temporarily succeeds. The alien thyroid cells are 

 destroyed by cytolysins (p. 31) in the serum and tissue liquids of 

 the animal. When a small part of a thyroid is left, it may undergo 

 great hypertrophy, and the same is true of the accessory thyroids, 

 frhe administration of extracts of the thyroid glands or the glands 

 themselves by the mouth brings about a cure, permanent so long as 

 the thyroid treatment is continued, in cases of myxcedema in man,) 

 and prevents the development of the symptoms in animals or 

 removes them when they have appeared, t The same is true of a 

 compound rich in iodine, the so-called thyroiodin, which has been 

 extracted from the organ.N Under this treatment the total metab- 

 olism, which in myxcedema is below the normal, is markedly in- 

 creased. This is partly due to an increase in the metabolism of 

 protein. An increase in the destruction of protein is also caused 

 in normal persons and in normal animals by feeding with thyroid 

 or with thyroid preparations. The excretion of nitrogen, carbon 

 dioxide, and phosphoric acid, and the intake of oxygen, are aug- 

 mented. But in spite of increased appetite the body-weight falls 

 off, and diarrhcea is often caused. For these reasons the use of 

 thyroid preparations to reduce weight in cases of obesity, without 

 evidence of thyroid insufficiency, is a dangerous remedy. For while 

 a fat man can very well spare a great deal of his fat, he cannot 

 spare much of his tissue-protein. That the gland exerts in some 

 way an important influence on the metabolism of proteins is also 

 indicated by other facts. The question whether the thyroid or 

 parathyroid is, in addition, concerned in the carbo-hydrate metab- 

 olism is at present the subject of discussion, but the data are 

 so contradictory that it would not be advisable to enter into the 

 matter here. 



(The ready response of the thyroid by hyperplasia or involution 

 to changes in the nutritive conditions is one of its most striking 

 characteristics! and further illustrates the significant role which it 

 plays in the cfiemical activities of the body. pThe thyroid swells 

 and shrinks almost as easilv and under almost as great a variety 

 of conditions as the spleenU One of the most interesting of the 

 physiological changes is the hyperplasia of the gland which is a 

 normal accompaniment of pregnancy. \ A pathological change of 



