CHAPTER VI 



THE REDUCTIO AD ABSURDUM OF WEISMANN'S THEORY 



(1907) 



There have of late years been abundant theories of inheritance 

 brought forward, but none has attracted greater attention than 

 that of Weismann, none has been so fully worked out ; and as 

 the distinguished author of the theory in the evening of his life 

 has given us this theory in a rounded and complete form, which 

 has, further, been admirably translated, 2 it will be well to take 

 this as a basis. 



Weismann accepts, as indeed he was one of the first to em- 

 phasize, that inheritance is conveyed by germ cells which have 

 from the first been set apart for reproductive purposes. These 

 germ cells as such take no part in the building up of the parental 

 individual of whose organism they form a part ; only when 

 liberated and fertilized do they proceed to multiply, giving rise 

 to one set of cells which form the body as a whole, and to another 

 smaller set — the germ cells. In other words, he holds that the 

 germ cells contain within them two constituents, the somatic 

 or body plasm and the germ plasm. The tissues built up bj 

 the somatic plasm are mortal, subject to death ; the gerrn 

 plasm is potentially eternal — it is carried onward from generatior 

 to generation. Here is the first weak point in Weismann's 

 argument — a false conception which vitiates the whole subsequent 

 train of thought. The germ plasm is not potentially eternal. 

 If, as already indicated, the individual human being derived 



1 Abstracted from article upon " Inheritance and Disease " in the System 

 of Medicine by Sir W. Osier, Bart., F.R.S., F.R.C.P., and T. McCrae, M.D., 

 F.R.C.P., Philadelphia, Lea Bros. & Co., vol. i., 1907, p. 36. 



2 August Weismann, The Evolution Theory, translated by J. Arthur 

 Thomson and Margaret R. Thomson. London, Ed. Arnold, 1904. 



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