PRESIDENTIAL ADDRESS. 89 
gvametoid, partly somatically differentiated. Now the 
gametoid aspect predominates, and the cells invade and eat 
into the tissues, undergo reducing or irregular divisions, 
and form clumsy gametes incapable of fertilising each 
other; now the somatic side preponderates and the cells 
differentiate more or less, forming, for instance, in certain 
eases, keratin and cell-nests. This uncontrolled and un- 
controllable, unbridled, incoordinate and chaotic cell-mass 
is cancer. Its occurrence I believe to be thus due to the 
recessive gametoid factors in a group of cells becoming able 
to exert their influence through failure of the dominant 
somatic factors to maintain fully their dominance. 
'Two questions require answering. One is, is there any 
evidence that recessive factors may in the progeny of so- 
matic cells eventually manifest themselves through failure 
of the dominant factors? The other question is, is there 
any evidence that the changes found in cancer are of a 
gametoid nature? 
As answer to the first question, may I mention a curious 
phenomenon in the case of my wife’s hair. This is dark 
brown, but occasionally she has noticed, and I have secured, 
an odd hair of much coarser texture and bright reddish 
colour. Being of Scotch extraction, it is clear that these 
are hairs of an individual with the vivid colouring well- 
known amongst that race. But how came they to appear 
on my wife’s head? The hairs of the head are derived from 
down-growths of the surface epithelium. This latter is 
derived from the epiblast. The epiblast is descended from 
the original fertilised ovum. The cells of the hair follicles, 
before producing a hair, have gone through an enormous 
number of generations since the epiblast first appeared. 
They all must at one time have possessed attributes in com- 
mon. How, then, does it come about that an occasional 
hair follicle produces a hair unlike its fellows? The 
