684. JULIAN S. HUXLEY 
had been a jockey.) His recovery was interesting for various 
reasons. ‘The mtolerance for all diets save milk he lost earlier 
than the other infantile symptoms. As regards purely mental 
symptoms his growth or redifferentiation was gradual and 
progressive, though with considerable rapid oscillations. 
It is therefore clear that the picture is not quite as simple 
as I have drawn it above. Hach stage is really in some ways 
dominant to the one below, subordinate to the one above, 
and if there has been a considerable degree of regression, the 
redifferentiation must apparently be by steps (although the re- 
gression itself is a sudden instantaneous process). In the normal 
adult each lower stage is kept in its proper place in the hierarchy, 
and most of the associations and types of reactions connected 
with it exist in posse only. When it is released from the 
inhibitory contrel of the processes associated with higher stages 
it becomes dominant, and then these potential associations, 
memories, and reactions become actual and functional again. 
Normally, since each stage of growth represents a necessary step 
towards the next stage, some of the reactions of each stage are 
functional even in the adult, as foundations for normal adult 
activity; but they are altered by the dominant higher processes 
to a form different from that which they would have if released 
from control. This is parallel, though not identical, with the 
behaviour of dominant and subordinate regions in regenera- 
tion (see later). Regression takes place suddenly to that 
stage whose system has been encouraged ; if the patient has 
dwelt upon a particular time of childhood, to the system 
associated with that time; if he has dwelt on mere release 
from control, to an infantile stage. But recovery must be by 
eradual building-up, as in physical development. 
Individual mental development is thus an epigenetic pro- 
cess ; and the different stages of this development are arranged 
in a functional hierarchy or series in which each stage is 
dominant to the one below, subordinate to the one above. 
1 The alternation of dominance seen in dual and multiple personality 
(Prince, 1908, 1920) is presumably based upon essentially the same principles, 
the difference being that typically the two systems are very evenly balanced, 
. 
