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THE AMERICAN NATURALIST [Vol. XLIX 



fluids after auto-transplantation. And it seems that a 

 perfect fulfilment of the second requirement might even 

 be able to overcome a deficiency in the first condition, the 

 specific adaptation between tissues and body fluids. This 

 seems at least to be the case, whenever a kidney is suc- 

 cessfully transplanted into another individual of the same 

 species and lives here for a long period of time. 



A peculiar resistance to foreign body fluids is appar- 

 ently shown by the germ cells. They represent in reality 

 individuals residing in a host organism of the same spe- 

 cies. In this case the host organism is nearly related to 

 but not identical with the individuality of the germ cells. 

 In some respects we have, therefore, here a condition com- 

 parable to one existing after homoiotransplantation of 

 tissues. And still the germ cells do not show any signs of 

 injury. There is, therefore, in germ cells as yet lacking 

 that substance which has a specific affinity to certain parts 

 of the body fluids, or through their situation the germ 

 cells are somehow protected against the injurious influ- 

 ence of these substances. 



Thus it comes about that through transplantation into 

 other individuals of the same species the potential im- 

 mortality of the ordinary tissues can not he demonstrated. 

 This applies to the tissues investigated so far. 10 How- 

 ever, it is quite possible that we may yet find that in the 

 case of certain tissues the life may be permanent even 

 after homoiotransplantation. It was furthermore think- 

 able that through serial transplantation, retransplanting 

 the tissue at an early date before the lymphocytes and con- 

 nective tissue had had a chance to seriously injure it, 

 better success could be obtained. Tn the case of the skin 



