88 SEX AND HEREDITY 



The " provisional hypothesis " which Darwin proposed 

 to account for this was that every cell in the body is 

 continually throwing off ultra-microscopical particles, 

 which he called gemmules, and which got into the blood 

 stream and were thus carried to the reproductive organs 

 and became stored up in the germ-cells. These latter were 

 in fact, in his view, nothing more nor less than little 

 packets of gemmules, and the development of the germ- 

 cell into the individual of the next generation consisted 

 in each gemmule growing into a cell like the 'one which 

 had produced it. 



Gait on looked at the stream of life from a different 

 point of view. He broke into the parent-germ-parent 

 chain at the germ or rather he denied the existence of a 

 chain at all, but looked upon the stream of life as a straight 

 line of germ-cells, giving off blind side alleys in each 

 generation the bodies of the organisms which we know. 



This view was much elaborated by Weismann, to whom 

 we are indebted for a more detailed conception of the 

 relation between the germ-plasm and the body-plasm 

 the former being of course the protoplasm (more particu- 

 larly, the nuclear material or chromatin) contained in 

 the germ-cells, while the body-plasm forms the substance 

 of the body cells. He pointed out that the germ-plasm 

 is potentially immortal, that is to say, it does not die 

 provided that its environment is of a suitable nature, 

 whilst the body-plasm is mortal. 



To a certain extent this proposition may be described 

 as a truism, since it is of course obvious that the living 

 substance of which all of us are composed is continuous 

 back to the beginnings of life on this globe, millions of 

 years ago. Such part of that living substance which has 

 entered into our bodily structure, however, is doomed 



