BRITISH ASSOCIATION. 305 



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 quantitative 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 4000 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 

 illustrate their pedigrees. Galton was beset by the same kind of 

 mistake when he promulgated his " Law of Ancestral Heredity." 

 With modern research all this has been cleared away. The allot- 

 ment of characteristics among offspring is not accomplished by the 

 exudation of drops of a tincture representing the sum of the character- 

 istics 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 proper- 

 ties depend on some phenomenon of arrangement. However that 

 may be, analytical breeding proves that it is according to the dis- 

 tribution 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 physiological meaning of that expression. An organism is pure- 

 bred when it has been formed by the union in fertilization 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 



