56 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



readily in mice than in rats or guinea pigs, because of the greater difficulty of 

 performing a perfectly sterile operation in the smaller animal. 



In transplantations of pieces of thyroid, striated muscle, xiphoid cartilage 

 with fat tissue, and of ovaries between not closely inbred mice, obtained 

 from different dealers, or from inbred D or C57 mice to the former, after 

 20 and 30 days the grades ranged between 1 and 2—, except in one trans- 

 plantation, in which the grade was 2. With the exception of the latter, the 

 results were therefore characterisitc of severe homoio-reactions. In no case 

 was ovarian tissue preserved. When grade 1 was given, neither the muscle nor 

 the thyroid transplant was preserved; only cartilage and perichondrium had 

 survived and the fat tissue was partly infiltrated with small vacuolated or 

 epithelioid phagocytic cells and with varying amounts of fibrous tissue and 

 lymphocytes; however, these reactions in the fat tissue were always much 

 diminished as compared with those in rats and guinea pigs, except in some 

 transplants in which polymorphonuclear leucocytes were more pronounced. 

 In general, the amount of fat tissue preserved was greater in the mouse than 

 in the two other species. In the case in which grade 2 was given, the thyroid 

 transplant, while small, was in a relatively good condition ; the center was 

 filled with dense hyaline tissue and the surrounding ring of acini was incom- 

 plete; also, the parathyroid was preserved. In the cartilage-fat transplant the 

 fat tissue was fairly well preserved but there was here some increase in fibrous 

 tissue and there were collections of lymphocytes. Parts of the transplanted 

 muscle tissue were preserved and embedded in fibrous tissue. 



In an additional series of experiments we exchanged thyroid, cartilage and 

 fat tissue, with or without bone or muscle tissue, between non-inbred mice and 

 inbred mice belonging to strains D, C57 and A. In these experiments the 

 grades also varied as a rule between 1 and 2— ; in a few cases, slightly better 

 grades (2/2—) were obtained. The reactions were usually more severe after 

 20 than after 12 days. Occasionally there was some lymphocytic infiltration in 

 the thyroid transplants ; in the fat tissue there was partial invasion by con- 

 nective tissue, vacuolated phagocytic cells and lymphocytes. 



Among the many experiments in which tissues were exchanged between 

 different strains of inbred mice, we may mention one set in particular, in 

 which thyroid, cartilage and fat tissue, with associated tissues, as well as pieces 

 of striated muscle or ovary were transplanted into each host and examination 

 took place after 20 days. In ten transplantations to different hosts the grades 

 varied in the individual cases between 1 and 2—. When grade 1 was given, 

 only the cartilage or parts of cartilage were preserved, but perichondrial re- 

 generation of cartilage could take place around necrotic areas. The fat tissue 

 as a rule was, to a variable extent, invaded by small vacuolated phagocytic cells 

 and by connective tissue; infiltration with lymphocytes varied in different 

 cases ; also the amount of preserved fat tissue was variable, but on the average, 

 the amount was greater in these transplantations in mice than in rats and 

 guinea pigs. There were also some collections of polymorphonuclear leuco- 

 cytes, especially in the fat tissue, and more prominently around fat cells which 

 were enclosed in fibrous tissue. The thyroid was either entirely replaced by 



