406 Mr. William Bate Hardy [April 6, 



It has been shown recently by a French physicist, M. Perrin,* 

 that by the use of minute amounts of salts one can give to the surface 

 energy of a solid a certain direction — one can fix in the surface layer 

 certain qualities which, for instance, define the electric properties of 

 the surface. The effect once produced, no amount of washing will 

 undo it ; the salt can be removed, the effect remains. So far as we 

 know, in the absence of active chemical intervention it will endure 

 for all time, always exerting a directive influence upon the molecular 

 events in its neighbourhood. In these experiments there is, it seems 

 to me, a real clue to the nature of the phenomena of rejuvenescence. 



Heredity. 



On the earth are some half -million different species of animals 

 and plants, each of which breeds true in virtue of what we call 

 heredity. Each species therefore represents a strain or line of 

 descent of living matter always growing, dividing, and increasing in 

 mass, like the little paramoecia we have already considered, each 

 striving to occupy the whole earth, and restrained in the attempt 

 only by the accident of death. 



The strains of living matter are separated from one another by a 

 wide gulf which we do not know how to bridge. Change of state 

 seems to be without effect. Continuous supplies of the richest food 

 will not convert a strain of dwarfs into giants. In the solemn words 

 of the Burial Service, " All flesh is not the same flesh, but there is 

 one kind of flesh of men, another flesh of beasts, another of fishes, 

 and another of birds." 



The nature of these differences in the kinds of living matter and 

 their mastery so that we may be able to control them is without 

 dou])t the most difficult and the most important problem which 

 science has attempted to solve : most difficult because it deals with a 

 form of matter much more complex than any which the chemist or 

 physicist so far has considered ; most important because on the solu- 

 tion of this problem depends the possibility of removing practical 

 medicine, politics, and morality from the domain of empiricism and 

 tradition to that of rational co-ordinate knowledge. 



To speak of a strain breeding true is a bald way of describing a 

 force so potent as heredity, so impish in its eccentricities. On the 

 Antarctic ice there aljounds a race of birds called })enguins. They 

 have never seen a tree since they first were penguins : they do not 

 fly, for their wings have been reduced to small flat paddles with 

 which they swim. Tlie l)ird cannot tuck its head under its wing, 

 because the wings are too shrunken ; but still, in mute worship and 

 touching fidelity to its forbears of thousands of years ago, when it 



Juurn. d. CJiem. Physique, ii. p. 61, and iii. p. 50. 



