648 INTERNAL SECRETION ENDOCRINE GLANDS 



the thyroid itself, or the thyroid plus the small internal pair of 

 parathyroids, was extirpated, the condition called cachexia 

 strumipriva was observed to supervene. The symptoms resemble 

 those of the disease known as myxcedema, in which the charac- 

 teristic anatomical change is an increase (a hyperplasia) of the 

 connective tissue in and under the true skin. Newly-formed connec- 

 tive tissue always contains an excess of mucoids, and for this reason 

 in the early stages of myxoedema there is somewhat more than the 

 usual amount of these substances in the subcutaneous tissue. The 

 skin is dry, and the hair falls off. The features are swollen and 

 heavy, and movements clumsy and trembling. As the disease 

 progresses the mental powers deteriorate too; the patient becomes 

 stupid and slow, and perhaps, at last, imbecile. When the gland 

 is so affected in early life that extensive atrophy of the true secreting 

 tissue occurs, a peculiar condition of idiocy (cretinism) results. 



In animals there is a great difference in the results of total ex- 

 cision of the thyroids, both between different groups and between 

 different individuals of the same group. In young animals the 

 symptoms come on more rapidly and are more severe than in old. 

 Monkeys develop symptoms resembling those of myxcedema. 



The older descriptions of the very acute onset of the symptoms 

 and the quickly fatal result in carnivorous animals were vitiated 

 by the circumstance that, for the anatomical reason already alluded 

 to, the parathyroids were also involved in the operation. Never- 

 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. 699). 



If a portion of the thyroid be left, or an autograft be made in any 

 part of the body, these effects are permanently obviated. Homoeo- 

 grafts, although they take, rarely survive and function. Working with 

 rabbits, Marine and Manley have found that thyroid autografts take 

 and grow when placed in any tissue, spleen and bone marrow being the 

 least favourable tissues, while the sex glands and the adrenals are 

 probably the most favourable. The extent of the growth of thyroid 

 autografts depends on the age of the animal, being more marked in 

 young animals, on the amount of the thyroid gland removed, and on the 

 administration or withholding of iodine. Thyroid homceografts rarely 

 succeed. In a series of 567 thyroid homceografts in rabbits, 92 per cent, 

 underwent absorption in ten to thirty days ; 6 per cent, remained active 

 from two to six months before being absorbed ; and 2 per cent, were 

 permanent and behaved in all respects like autografts. The outlook 

 for the therapeutic application of thyroid grafts in the treatment of 

 thyroid insufficiencies is therefore not hopeful, unless some means is 

 discovered to overcome the power of the host to destroy foreign 

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

 even temporarily succeed. The alien thyroid cells are destroyed by 

 cytolysins (p. 31) in the serum and tissue'liquids of the animal. 



