THE PARATHYROID GLAND AND ITS DISEASES 507 



them in small laboratory animals, that we know practically nothing of the 

 structural changes which they may undergo in different experimental con- 

 ditions. It would be interesting and important to find out whether they 

 respond, in the same way as the thyroid gland, to variations in diet, tem- 

 perature, unhygienic conditions, etc. 



Like the thyroid gland, and probably for similar reasons the para- 

 thyroids show the widest variations in structure, so that the interpretation 

 of our histological findings is very difficult. At present, there are no 

 known histological criteria, on which we may, with confidence, gauge the 

 activity of the parathyroid glands. 



