310 BIOLOGY AND ITS MAKERS 
time, of the germinal substance, is a conception of very great 
extent, and now underlies all discussion of heredity. 
In order to comprehend it, we must first distinguish 
between the germ-cells and the body-cells. Weismann 
regards the body, composed of its many cells, as a derivative 
that becomes simply a vehicle for the germ-cells. Owen’s 
distinction between germ-cells and body-cells, made in 1849, 
was not of much importance, but in the theory of Weismann 
it is of vital significance. The germ-cells are the particular 
ones which carry forward from generation to generation the 
life of the individual. The body-cells are not inherited di- 
rectly, but in the transmission of life the germ-cells pass to 
the succeeding generation, and they in turn have been inher- 
ited from the previous generation, and, therefore, we have 
the phenomenon of an unbroken connection with all previous 
generations. 
When the full significance of this conception comes to us, 
we see why the germ-cells have an inherited organization of 
remarkable complexity. This germinal substance embodies 
all the past history of the living, impressionable protoplasm, 
which has had an unbroken series of generations. During 
all time it has been subjected to the molding influence of 
external circumstances to which it has responded, so that 
the summation of its experiences becomes in some way 
embedded within its material substance. Thus we have 
the germinal elements possessing an inherited organization 
made up of all the previous experienccs of the protoplasm, 
some of which naturally are much more dominant than the 
others. 
We have seen that this idea was not first expressed by 
Weismann; it was a modification of the views of Nussbaum 
and Hertwig. While it was not his individually, his con- 
clusions were apparently reached independently. This idea 
was in the intellectual atmosphere of the times. Several 
