Chapter 2 

 Autogenous and Homoiogenous Transplantations 



We shall now compare the reactions against autogenous and homoi- 

 ogenous transplants, first in rats and guinea pigs and then in mice 

 and chickens, and we shall consider the transplantation of thyroid, 

 cartilage and fat tissue, and later also that of striated muscle and a few other 

 tissues. 



1. Autogenous transplantation of thyroid in rat and guinea pig. After auto- 

 transplantation of thyroid in rat, as well as in guinea pig, there remains at 

 first a ring of preserved acinar tissue around a central necrotic zone; the 

 latter is smaller in the rat. Blood vessels and connective tissue cells are at- 

 tracted by the transplant and the vessels and fibroblasts penetrate towards 

 the necrotic center, where they form a loose, vascularized connective tissue. 

 In the guinea pig, this takes the form of a distinct myxoid zone, situated be- 

 tween the necrotic center and the peripheral ring of living acini, whereas, 

 in the rat this ringlike myxoid area is not so distinct. The organization of 

 the center in the latter species is usually completed by the 15th day, when 

 also the necrotic center of the parathyroid has been replaced by connec- 

 tive tissue ; at this time, furthermore, accompanying the fibroblasts and vessels, 

 a few lymphocytes or very small groups of lymphocytes may be seen in 

 the central or peripheral connective tissue of the graft. In the first week 

 after transplantation the colloid may be lacking in the acini of the transplant 

 and phagocytes may contribute to the destruction of the latter, but after two 

 weeks this colloid has been replaced by newly-formed colloid wihin the acini, 

 the epithelium of which is rather low. The number of fibroblasts which move 

 towards the center is, on the whole, rather small, and the few lymphocytes 

 which may accompany these cells are probably attracted by non-specific fac- 

 tors, perhaps by the necrotic tissue ; in other cases, foreign bodies may attract 

 some lymphocytes. Around the 4th week, or somewhat earlier, the transplanted 

 thyroid shows a curved structure. At this time an interesting change takes 

 place, leading to the disappearance of the central connective issue which had 

 been formed by the organization of the central necrotic material. This con- 

 nective tissue, which may have become fibrous or hyaline, is either pushed out 

 of the transplant into the neighboring tissue or it is invaded and absorbed by 

 new fibroblasts of the host, although a small amount of hyaline material may 

 remain within the inner ring of acini. The acini are surrounded by well-formed 

 capillaries, not necessarily accompanied by fibroblasts. Towards the end of the 

 5th week, lymphocytes are either entirely lacking, or, in certain cases, are 

 present in small collections. Between the 40th and 60th day the transplant 

 begins to resemble the normal thyroid, but the epithelium is lower than in the 

 original acini and a very small amount of fibrous tissue may be found between 



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