458 SCIENTIFIC THOUGHT. 



This provisional statement, which emphasises the now 

 generally recognised difference between the germ-sub- 

 stance and the body-substance, requires, however, two 

 further qualifications in order to embrace the great 

 characteristic facts of life and death as modern em- 

 bryology and the phenomenon of descent have unfolded 

 them. 



Only in rare instances can we observe the continuity 

 of cells i.e., of those organisms which, so far as our 

 knowledge goes, form the ultimate units of living matter. 

 Weismann recognised, as did the great botanist Nageli, 

 and long before both of these the philosopher Herbert 

 Spencer, that though in the cell, with its nucleus and 

 protoplasm, we may have arrived at the last microscop- 

 ically visible independent units of life, we must with 

 the atomic theory in chemistry assume the existence 

 of much smaller units in all living matter, compared with 

 which even the nucleus of the cell is a very complex 

 aggregate. If the continuity of life is dependent upon 

 that of an underlying living substance, this substance 

 must be only an infinitesimal portion of any visible cell 

 54. or nucleus. The conception of a continuous germinal 



Germ- 



Cimaand substance has thus taken refuge in the more refined 

 y. 



plasma. conception of a germ-plasma, as distinguished from the 



body or somatic plasma : the former is immortal within 



the limits of the conditions of organic life, the latter is 



Naturforscher - versammlung at 

 Salzburg, reprinted in ' Essays upon 

 Heredity,' tran*l. by Poulton and 

 others, Oxford 1889 ; see also the 

 ' Studies in the Theory of Descent,' 

 transl. by Meldola, 2 vols., 1882, 

 and the earlier essays of Weismann 

 mentioned in the preface, p. viii.), 



has become both scientifically and 

 popularly recognised and debated, 

 are given in Geddes and Thomson, 

 ' The Evolution of Sex,' p. 93 ; also 

 in M. Delage's great work, p. 349, 

 &c., and in Wilson, 'The Cell,' p. 

 295, &c. 



