758 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



thyroid becomes enlarged at puberty, during the menses, and during 

 pregnancy, and in thyroidectomized young animals the sexual glands 

 fail to develop properly. 



2. With the Adrenal Glands. (See page 746.) 



3. With the Pituitary Body. After removal of the thyroid, the pitu- 

 itary becomes greatly altered and enlarged, particularly the pars an- 

 terior, in which it is not uncommon to find that a certain amount of 

 vesicles containing colloid, not unlike those of the thyroid, become devel- 

 oped. This colloid material, however, does not contain iodine. It is said 

 that this increase of the pituitary after thyroidectomy does not occur if 

 thyroid extract be administered. Increased activity of the pars inter- 

 media of the pituitary is also quite plain. These facts Avould at first 

 sight seem to indicate that the pituitary and the thyroid can act vica- 

 riously, but this is very doubtful, for it has not been found that pitu- 

 itary extract has any beneficial effect in the treatment of goiter and myx- 

 edema. Nevertheless the association in function of the two glands must 

 be more or less close, not alone for the above reasons, but also because they 

 are both associated to much the same degree with the sexual organs, 

 and both act on the higher functions of the nervous system in much the 

 same manner. 



4. With the Thymus Gland. The persistence of the thymus in ex- 

 ophthalmic goiter, as well as the anatomic and embryologic relationship 

 between thymus and thyroid, is taken to indicate some close relationship. 



THE PARATHYROIDS 



Experimental Parathyroidectomy 



Experimental parathyroidectomy yields results which vary in dif- 

 ferent groups of animals, undoubtedly because of the fact that in some, 

 such as the rat and rabbit, accessory parathyroids may exist. In . gen- 

 eral, however, it has been found that if more than two of the four 

 parathyroids be removed, very definite and pronounced nervous symp- 

 toms soon supervene and if all four glands be removed, a quickly fatal 

 result is inevitable. The most acute symptoms are exhibited by the 

 carnivora. They may not be apparent for a day or two after the opera- 

 tion, although during the period the animal is in a depressed state, re- 

 fusing food and losing weight rapidly. The muscles are also more or less 

 stiff during this stage. When more definite symptoms appear, they con- 

 sist of a marked abnormality of muscular contraction, leading to the 

 occurrence of fibrillar contractions, or tremors and, later, to cramp-like 

 and clonic contractions. When spontaneous movements are made, a 



