TH YROIDS A ND PA RA TH YROIDS 633 



The excit ibility of the vasoconstrictor mechanism is said to be 

 increased. The exact significance of these symptoms is unknown 

 It has been suggested that the loss of the parathyroid function is 

 in some way associated with an augmentation of the irritability of 

 the whole sympathetic system (Hoskins). rThe administration of 

 calcium completely relieves the symptoms, and by its use death may 

 be long or perhaps indefinitely postponed (W. G. MacCallum). The 

 mode of action of the calcium has not been made clear as yet) It 

 does not seem to be so efficacious in rabbits as in dogs (Arthus). 



/Thyroidectomy.4fThe symptoms that follow removal of the 

 thyroid alone are perfectly different^ The metabolic disturbance is 

 eventually, in most animals, not le^s 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, and is completely corrected by the administration of 

 thyroid substance. 1 While no animals which have been examined 

 survive the total removal of the parathyroids, certain species 

 e.g., the goat are but slightly affected by thyroidectomy, and 

 survive indefinitely. / In man, before the consequences of thyroid- 

 ectomy were known,* the whole gland was not infrequently excised 

 for goitre. | ftf the parathyroids happened also to be completely 

 involved in the operation, death quickly followed J (But where only 

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

 parathyroids, was extirpated, the condition called cachexia 

 strumipriva was observed to supervene. J /The symptoms resemble 

 those of the disease known as myxcedeina, 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 myxcedema there is somewhat more than the 

 usual amount of these substances in the subcutaneous tissue, f The 

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

 heavy, the 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- 



