560 A MANUAL OF PHYSIOLOGY . 



Thyroidectomy. The symptoms that follow removal of the 

 thyroid alone are perfectly different. The metabolic disturbance 

 is eventually, in most animals, not less far-reaching than that 

 which ensues when the parathyroids are alone excised. But it is 

 far more chronic, reveals itself by totally distinct changes, is 

 not amenable to calcium, but is completely corrected by the 

 administration of thyroid substance. While no animals which 

 have been examined survive the total removal of the para- 

 thyroids, certain species e.g., the goat are but slightly affected 

 by thyroidectomy, and survive indefinitely. In man, before the 

 consequences of thyroidectomy were known, the whole gland was 

 not infrequently excised for goitre. If the parathyroids hap- 

 pened also to be completely involved in the operation, death 

 quickly followed. But where only the thyroid itself, or the 

 thyroid plus the small internal pair of parathyroids, was extir- 

 pated, the condition called cachexia strumipriva was observed to 

 supervene. The symptoms resemble those of the disease known 

 as myxcedema, in which the characteristic anatomical change is 

 an increase (a hyperplasia) of the connective tissue in and under 

 the true skin. Newly-formed connective tissue always contains 

 an excess of mucin, and for this reason in the early stages of 

 myxoedema there is somewhat more than the usual amount of 

 that substance in the subcutaneous tissue. The skin is dry, 

 and the hair falls off. The features are swollen and heavy, 

 the movements clumsy and trembling. As the disease pro- 

 gresses 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 myx- 

 oedema. 



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. 

 Nevertheless, the consequences of complete removal of the thy- 

 roid 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. 593). If a 

 portion .of the thyroid be left, or a graft be made of some thyroid 



