26 The Endocrine Organs 



of the parathyroids are ligatured (Thompson, Leighton and Swarts). 

 An observation which has frequently been made after parathyroid- 

 ectomy is the occurrence of changes in the hair and nails, and also in 

 the growth and structure of the bones and teeth. These changes are, of 

 course, only seen if the animals survive the operation for some time. As 

 Erdheim has shown, the calcification of the teeth is delayed and imper- 

 fect, and they are unusually brittle. In the skeleton the bones remain 

 smaller than in the controls; also the healing of fractures is delayed. 

 If these changes are the direct result of the removal of the parathyroids, 

 there is obviously reason for believing that the parathyroids influence 

 calcium metabolism in some way which is not understood ; a further founda- 

 tion for this is met with in the fact that more than one observer has 

 described an increase of calcium excretion in parathyroidectomised animals. 

 In connexion, however, with this subject, other facts appear to point in 

 the opposite direction, since many cases of osteomalacia have been found 

 to be associated with hyperplasia (adenoma) of one of the parathyroids, and 

 therefore presumably with a condition of hyperparathyroidism. 



MacCallum and Voegtlin found that the effects of parathyroidectomy 

 could be removed by injection of extract of parathyroid. The extract has 

 also been used with some success in man by Halsted. Extract of pituitary 

 is said by Ott to have a similar effect. The same result was obtained by 

 MacCallum from the administration of calcium salts, both subcutaneously 

 and by the mouth ; he regards tetany as caused by a diminished calcium 

 content of the blood. According to Biedl, however, these salts do not 

 prolong life after the operation ; and in my own experience they may 

 altogether fail either to prevent or alleviate post-operative tetany. Accord- 

 ing to Carlson and Jacobson, the action of calcium salts, when it occurs, 

 is merely like that of other substances which decrease the excitability of 

 the nervous system. 



In man, cataract is often found to be associated with chronic tetany. 



PHYSIOLOGICAL EFFECTS OF PARATHYROID EXTRACT 



Probably largely owing to the difficulty of obtaining enough material, 

 very few observations have been made on the physiological effects of 

 injections of parathyroid extracts. Ott finds that when injected intra- 

 venously they have an entirely different effect from those of thyroid 

 (see p. 35). He states that the blood-pressure is first raised, then lowered ; 

 that the rate of respiration is increased ; that they are diuretic, acting 

 directly on the renal epithelium, and that in large doses they have the effect 

 of lowering the body temperature. Also that applied locally the extracts 

 increase the extent of the contraction both of intestines and uterus, and 

 dilate the pupil. These statements await confirmation. 



