PRESIDENTS ADDRESS. 7 
research all this has been cleared away. The allotment of character- 
istics among offspring is not accomplished by the exudation of drops 
of a tincture representing the sum of the characteristics of the parent 
organism, but by a process of cell-division, in which numbers of these 
characters, or rather the elements upon which they depend, are sorted 
out among the resulting germ-cells in an orderly fashion. What these 
elements, or factors as we call them, are we do not know. That they 
are in some way directly transmitted by the material of the ovum and 
of the spermatozoon is obvious, but it seems to me unlikely that they 
are in any simple or literal sense material particles. I suspect rather 
that their properties depend on some phenomenon of arrangement. 
However that may be, analytical breeding proves that it is according 
to the distribution of these genetic factors, to use a non-committal term, 
that the characters of the offspring are decided. The first business of 
experimental genetics is to determine their number and interactions, 
and then to make an analysis of the various types of life. 
Now the ordinary genealogical trees, such as those which the stud- 
books provide in the case of the domestic animals, or the Heralds’ 
College provides in the case of man, tell nothing of all this. Such 
methods of depicting descent cannot even show the one thing they are 
devised to show—purity of ‘ blood.’ For at last we know the physio- — 
logical meaning of that expression. An organism is pure-bred when it . 
has been formed by the union in fertilisation of two germ-cells which 
are alike in the factors they bear; and since the factors for the several 
characteristics are independent of each other, this question of purity 
must be separately considered for each of them. A man, for example, 
may be pure-bred in respect of his musical ability and cross-bred in 
respect of the colour of his eyes or the shape of his mouth. Though 
we know nothing of the essential nature of these factors, we know 
a good deal of their powers. They may confer height, colour, shape, 
instincts, powers both of mind and body—indeed, so many of the 
attributes which animals and plants possess, that we feel justified in 
the expectation that with continued analysis they will be proved to be 
responsible for most if not all of the differences by which the varying 
individuals of any species are distinguished from each other. I will 
not assert that the greater differences which characterise distinct Species 
are due generally to such independent factors, but that is the conclusion 
to which the available evidence points. All this is now so well under- 
stood, and has been so often demonstrated and expounded, that details 
of evidence are now superfluous. 
But for the benefit of those who are unfamiliar with such work let me 
briefly epitomise its main features and consequences. Since genetic 
factors are definite things, either present in or absent from any germ- 
cell, the individual may be either ‘ pure-bred ’ for any particular factor, 
