38 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



some of them. In the lymph vessels, no lymphocytes, or only a few, may be 

 seen. As in the rat, so too in the guinea pig the ingrowth of fibroblasts is 

 limited and a loose connective tissue forms in the center adjoining the thyroid; 

 but the latter formation, assuming the shape of a ring, is more pronounced 

 here than in the rat. Also in the guinea pig the central fibrous tissue is elimin- 

 ated after some time, and in both rat and guinea pig the blood vessels are at- 

 tracted by autogenous substance ; this conclusion is based on the fact that the 

 vascularization is more marked in autogenous than in homoiogenous trans- 

 plants ; in addition, in the former, lymphocytes are lacking or slight in number. 

 In rat as well as in guinea pig the injury to the acini and the destruction of 

 colloid are gradually repaired and the transplants assume more and more the 

 character of the normal gland. The activity of the connective tissue and 

 lymphocytes is, therefore, restrained around and in autogenous thyroid grafts 

 and this condition is best suited for the restoration of the normal tissue rela- 

 tions and of the normal structure of such transplants. 



2. Homoiogenous transplantation of the thyroid in rat and guinea pig. 

 The intensity of this reaction depends largely on the relationship between host 

 and donor. In the rat, we carried out, therefore, three series of experiments, in 

 which the average relationship was somewhat varied; the probability that a 

 distant relationship existed between donor and host was greater in series B 

 than in series A; in both of these series white rats were used. In series C, 

 tissues of white rats were exchanged with those of cream and hooded rats. In 

 all of these series the same factors co-operated in inflicting damage on the 

 transplant, namely, (1) the action of the bodyfluids of the host, (2) the in- 

 creased invasion by fibroblasts and lymphocytes and the increased production 

 of fibrous or fibrous-hyaline tissue, which later interfered with the nutrition 

 of the transplant and injured it by exerting pressure on it, and (3) the dimin- 

 ished supply of blood and lymph vessels, which also diminished the nourish- 

 ment of the transplant. In series C the intensity of the reaction was greatest, 

 and in series A it was slightly greater than in series B. In both the latter series 

 the maximum of the reaction was obtained between the 20th and 30th day 

 after transplantation, but in series B, where there was probably, on the aver- 

 age, a nearer relationship between the different rats than in series A, an im- 

 provement in the average condition of the transplants was observed from then 

 on ; this was lacking in series A and C. 



In series A and B, at first conditions were similar. Between the 1st and 8th 

 days, two or three layers of acini were preserved in a number of instances, but 

 in others they were less well preserved ; the acini were small and the colloid 

 had been lost in many of them, while in others it was still present. Some 

 capillaries grew through the ring of acini and mitoses were seen in the acinus 

 cells. The necrotic center was organized by not very dense, small-celled con- 

 nective tissue or by very dense fibrous tissue, or in certain cases some necrotic 

 material was still left and was at least partly taken up by phagocytes. Hemor- 

 rhages from the rupture of the newly-formed capillaries may have occurred. 

 From the 6th day on, lymphocytes appeared in series A, while in series B they 

 accumulated somewhat later. They were carried to the transplant first by way 



