6 PRESIDENT’S ADDRESS. 
a chicken or how a Sweet Pea from its ovule and its pollen grain 
produces another Sweet Pea, we at least can watch the system 
by which the differences between the various kinds of fowls or 
between the various kinds of Sweet Peas are distributed among the 
offspring. By thus breaking the main problem up into its parts 
we give ourselves fresh chances. This analytical study we call 
Mendelian because Mendel was the first to apply it. To be sure, he 
did not approach the problem by any such line of reasoning as I 
have sketched. His object was to determine the genetic definite- 
ness of species; but though in his writings he makes no mention of 
inheritance it-is clear that he had the extension in view. By cross- 
breeding he combined the characters of varieties in mongrel individuals 
and set himself to see how these characters would be distributed among 
the individuals of subsequent generations. Until he began this analysis 
nothing but the vaguest answers to such a question had been attempted. 
The existence of any orderly system of descent was never even sus- 
pected. In their manifold complexity human characteristics seemed 
to follow no obvious system, and the fact was taken as a fair sample 
of the working of heredity. 
Misconception was especially brought in by describing descent in 
terms of ‘blood.’ The common speech uses expressions such as 
consanguinity, pure-blooded, half-blood, and the like, which call up a 
misleading picture to the mind. Blood is in some respects a fluid, 
and thus it is supposed that this fluid can be both quantitatively and 
qualitatively diluted with other bloods, just as treacle can be diluted 
with water. Blood in primitive physiology being the peculiar vehicle 
of life, at once its essence and its corporeal abode, these ideas of 
dilution and compounding of characters in the commingling of bloods 
inevitably suggest that the ingredients of the mixture once combined are 
inseparable, that they can be brought together in any relative amounts, 
and in short that in heredity we are concerned mainly with a quantita- 
tive problem. ‘Truer notions of genetic physiology are given by the 
Hebrew expression ‘ seed.’ If we speak of a man as ‘ of the blood- 
royal ’ we think at once of plebeian dilution, and we wonder how much 
of the royal fluid is likely to be ‘in his veins’; but if we say he is 
‘ of the seed of Abraham’ we feel something of the permanence and 
indestructibility of that germ which can be divided and scattered among 
all nations, but remains recognisable in type and characteristics after 
4,000 years. 
I knew a breeder who had a chest containing bottles of coloured 
liquids by which he used to illustrate the relationships of his dogs, 
pouring from one to another and titrating them quantitatively to illus- 
trate their pedigrees. Galton was beset by the same kind of mistake 
when he promulgated his ‘ Law of Ancestral Heredity.’ With modern 
