THE THYROID APPARATUS 85 



Nearly all authors are agreed that the healing-in of the 

 transplanted organ is preceded by a degenerative process, slight 

 at the periphery, but becoming more intense towards the centre, 

 where it culminates in complete necrosis. Soon blood-vessels find 

 their way from the periphery into the interior of the organ, which 

 shows a comparatively healthy peripheral zone passing into a 

 granulation zone, and a necrosed centre. Regeneration starts 

 in the peripheral follicles, and groups and rows of epithelial cells 

 appear, which are transformed into follicles. The granulation 

 tissue is replaced by glandular substance, while the necrosed 

 centre becomes a connective tissue scar. Finally, as the organ 

 becomes completely healed in and the vascularization improves, it 

 shows a structure precisely similar to that of the normal thyroid. 



Christiani showed, and his results were confirmed by those 

 of Salzer, that the healing-in of the implanted gland does not 

 take place in the same way in thyroidectomized as in normal 

 animals. After extirpation, the process is more rapid and 

 vascularization proceeds so quickly that about three weeks after 

 transplantation the gland is large in size and proliferates actively ; 

 a condition which, in the normal animal, is not reached until 

 seven to eight weeks after transplantation. Some degree of 

 difference is apparent for five to six months. It is obvious 

 that the rapid healing-in of the transplanted thyroid in 

 the case of the thyroidless animal is due to the more rapid 

 vascularization. Thus it appears that an early physiological 

 demand upon the function of the organ promotes its 

 rapid healing-in. Christiani also found that portions of 

 thyroid implanted into the ear of normal rats, healed in well ; 

 while in the case of animals to which thyroid tabloids were given, 

 only cicatricial tissue with no trace of glandular structure was 

 found at the site of implantation. He concludes from this that 

 the physiological demand of the organism upon the thyroid 

 function facilitates and hastens the reorganization of the trans- 

 planted tissue, and he agrees with Salzer that the large healthy 

 implanted gland of the thyroidectomized animal is an instance 

 of vicarious hypertrophy. 



The rapid healing-in of the implanted thyroid is accompanied 

 by equally favourable results in regard to its function. Imme- 

 diately after transplantation, the implanted organ is merely & 

 chemical storehouse of active thyroid substances ; with increasing 

 regeneration, however, it is gradually enabled to fulfil the com- 

 plete function of the normal thyroid gland. For this reason, 

 animals having one implanted lobe, but which are otherwise 

 thyroidless, may live for months without showing symptoms of 

 suppression. Payr found that after extirpation of the spleen, 

 into which the thyroid had been transplanted, several animals 

 developed not only post-operative tetany, due to removal of the 

 parathyroids, but also cachexia (emaciation, roughness of the 

 coat, falling of the hair). 



