4 THE THYROID AND 



left varied in different animals. One bitch which 

 had lost two-thirds of her total thyroid became 

 pregnant by a healthy male, and all her whelps had 

 enormous goitres, a fact which has also been 

 observed by Edmunds. 



Histological examination of the portion remaining 

 shows a sequence of changes remarkably like those 

 occurring in exophthalmic goitre, namely, distension 

 and irregular shape of the vesicles, with watery fluid 

 instead of colloid, and columnar epithelium instead 

 of cubical. 



REMOVAL OF PARATHYROIDS. 



The variation in the symptom-complex following 

 on thyroidectomy, and the variability of response 

 to thyroid feeding, both depend on any coincident 

 injury to the parathyroid glands. For many years 

 these glands passed unrecognized, and most of the 

 effects attributed above to removal of the thyroid 

 are as a matter of fact due to loss of the parathyroids. 

 These are two pairs of small glands lying behind the 

 lateral lobes of the thyroid close to the trachea, not 

 easily distinguishable from the thyroid except by 

 the microscope, when they are seen to consist of 

 columns of polygonal cells with no regular arrange- 

 ment into acini, and secreting no colloid. One pair 

 was discovered by Sandstrom in 1880, and the 

 functions were investigated by Gley in 1892 ; but 

 the second pair was not recognized till Kohn's 

 monograph appeared in 1895. A number of 

 physiologists have since described the effects of 

 removal (Vassali and Generali, Edmunds, Moussu). 



