646 INTERNAL SECRETION ENDOCRINE GLANDS 



and in man, and this pair of parathyroids is much larger than the 

 ether. In carnivorous animals, as the dog and cat, the anterior 

 pair of parathyroids is closely adherent to the thyroid capsule. 

 The superior, posterior, or internal pair, both in herbivora and carni- 

 vora, is always very closely associated with the capsule of the 

 thyroid, and frequently embedded in the substance of the gland. 

 The consequence of this arrangement is that in the older experiments 

 the chief masses of parathyroid tissue were much more likely to 

 escape removal with the thyroid in the case of herbivorous than in 

 the case of carnivorous animals. 



But even in one and the same species considerable variations may 

 exist. It is easy to see, then, that in removing the thyroid the 

 parathyroids would sometimes be completely removed as well, 

 while at other times all or some of the parathyroid tissue would be 

 spared. Add to this that sporadic masses of thyroid tissue (acces- 

 sory thyroids), often existing as far down as the root of the aorta 

 (always, indeed, in certain animals e.g., the dog), must necessarily 

 be spared in the most complete thyroidectomy, and it will cease to 

 excite surprise that the symptoms and pathological changes de- 

 scribed after that operation should have been so various and so 

 contradictory. We know now that the parathyroids are perfectly 

 distinct organs from the thyroid in development, in structure, in 

 function, and in the consequences of their removal. The para- 

 thyroids, for instance, contain no iodine, while iodine is a character- 

 istic constituent of the thyroid. Nor do the parathyroids show any 

 compensatory hypertrophy when the thyroid alone is excised, or 

 any changes which would indicate a definite relation to, still less, an 

 active participation in, the pathological processes occurring in the 

 thyroid in goitre. This does not mean, however, that there are 

 no points of contact between the functions of the two glands. The 

 more the matter is probed, the more clearly does it appear that none 

 of the organs is quite independent of the rest, and the reciprocal 

 relations of the ductless glands are probably of exceptional im- 

 portance. But the premature attempts which have been made, 

 in the absence of a sufficiency of exact data, to represent their 

 mutual influence by crude schemata, have retarded rather than 

 advanced our knowledge, and need not be referred to here. 



Parathyroidectomy. Total extirpation of the parathyroids is 

 followed by a train of acute symptoms, ending fatally, as a rule in 

 from one to ten days. The typical nervous symptoms following the 

 operation are those of ' tetany ' (tetania parathyreopriva), and the 

 tetany which used to be included among the consequences of re- 

 moval of the thyroid is now known to be due to the simultaneous 

 excision of the parathyroids (Kocher). A cat, after the combined 

 operation, is perfectly well on the first day. On the second day a 

 curious shaking of the paws is seen, tremors of central origin soon 



