60 THE CONTROL OF LIFE 



gives rise to the hen and to the eggs which the hen's 

 body contains. So we see that the parent is rather the 

 trustee of the germ-plasm (the germinal basis of the 

 specific organisation) than the producer of the child. 

 In a new sense the child is a chip of the old block. Or 

 as Professor Bergson puts it in less static metaphor, 

 " Life is like a current passing from germ to germ through 

 the medium of a developed organism." This continuity 

 of the germ-plasm, by cell-division after cell-division, 

 along a lineage of unspecialised cells, explains the 

 inertia of the main mass of the inheritance, which is 

 carried on, as we have seen, with little change, as it 

 were en bloc, from generation to generation. Men do 

 not gather grapes off thorns, or figs oS thistles. Similar 

 material to start with ; similar conditions in which to 

 develop ; therefore like begets like. 



(b) The second very important modern idea, which 

 we owe to Mendel and Professor de Vries, is that of 

 unit-characters already alluded to. Some have com- 

 pared its importance to that of the Atomic Theory in 

 chemistry. An inheritance is, in part, built up of 

 .^merous, more or less clear-cut, crisply defined, non- 

 blending characters, which are continued in some of 

 the descendants as discrete wholes, neither merging 

 nor dividing. A definite type of very intelligent dwarf 

 has been known to reappear for four or five generations. 

 The persistence of the Hapsburg lip is a well-known 

 instance of a trivial unit-character that came and stayed. 

 An abnormal peculiarity like having six fingers may 

 defy dislodgment for six generations. These unit- 



