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THE AMERICAN NATURALIST [Vol. XLIX 



in germ cells may not also be specific, although different 

 chemicals produce apparently the same results. May 

 there not in germ cells, just as in somatic cells, exist a 

 difference in the mode of production of these lesions 

 through the different substances and consequently a speci- 

 ficity in the acquired lesion, notwithstanding the appar- 

 ently unspecific character of the lesion? Our work makes 

 it possible that this question which seems of considerable 

 theoretical interest may be solved in a similar manner as 

 in the case of the somatic cells, viz., through testing the 

 immunity produced through the action of chemical sub- 

 stances. 



Summaey 



1. It is shown that evidence similar to that which makes 

 probable the potential immortality of protozoa and germ 

 cells also exists in the case of somatic cells of metazoa. 

 As far as the protozoa are concerned, the discussion does 

 not, as seems to be assumed, concern their potential im- 

 mortality so much as the question whether protozoa cor- 

 respond to germ or to somatic cells of metazoa or repre- 

 sent perhaps a combination of both. 



2. While in the case of tumor cells the potential immor- 

 tality of somatic cells has been demonstrated as definitely 

 as the character of the problem will ever permit, the diffi- 

 culties standing in the way of a similar demonstration in 

 the case of certain other somatic cells and the means of 

 overcoming these difficulties are analyzed. It is partic- 

 ularly shown that chemical differences existing between 

 the body fluids of individuals belonging to the same spe- 

 cies are the basis of these difficulties, and that as a result 

 of these differences the metabolism of cells in a new envi- 

 ronment is modified in such a way that the behavior of 

 connective tissue cells and of lymphocytes is altered, and 

 that as a result of these alterations the death of the tissue 

 is brought about where it could probably have lived indef- 

 initely. Besides altering the character of the body fluids, 

 transplantation of tissues furthermore has usually an 

 additional injurious effect ; it changes the way in which 

 nourishment is carried to the transplanted cells, and this 



