FINAL CONCLUSIONS	439
asymmetrical 2-distribution fit much more closely (x^2=3i*24;
P = -051, i.e. just over I in 20).
It may be of interest to speculate what influences can reasonably
account for the divergences that remain discernible. As the
analysis of variance indicates, some of the additional spreading in
the total figures is caused by the pooling of heterogeneous groups.
But other causes are unquestionably at work.
In the component curves, as we have already noted, the most
conspicuous deviations from normality consist in a heaping of
frequencies near either tail end and to a less extent near the centre.
Instances of the more extreme types, and instances of the well-
balanced type, are more numerous than a perfect normal distribu-
tion would allow ; and the excess appears most marked among the
older persons. An examination of the individual case-histories
suggests at least two explanations. First of all, every large and
random group must inevitably contain several persons who present
mild but definite pathological symptoms : one of the adult intro-
verts, for example, was subsequently diagnosed as a case of dementia
prsecox ; three of the extraverts were subsequently treated for
hysteria ; several others were noted as cases of suspected glandular
disturbance (e.g. there were three instances of definite hyper-
thyroidism among the adult and adolescent extraverts and as many
as 18 cases suggestive of mild hypothyroidism or mild hyperpituitar-
ism among the adult introverts; * high blood pressure' was
reported in 6 cases, including i hyperthyroid).^1 Among the
children, pathological cases were rarer : but at least 5 showed symp-
toms of mild chorea (4 girls aged 8-10, I boy aged n). Secondly,
among those exhibiting no discernible pathological symptoms, the
more extreme temperaments seem often to have undergone a self-
magnifying process, which has had a cumulative effect as the person
has grown older. As a result of habit and of the repeated reactions
of social intercourse, the introvert tends to become more strongly
and more generally introverted, and the extravert, instead of being
progressively suppressed, often develops an aggressive attitude that
grows more and more defiant and more and more obstinately fixed.
Possibly a similar tendency towards an all-round self-consistency
operates in the moderate types : those who from the outset possess
^1 With a small group of 35 male students we found a correlation of ^54
between systolic blood pressure and extraversion, '23 between extraversion
and weight, and -41 between systolic blood pressure and weight: (the latter
figures are of interest as suggesting that correlation of the so-called cyclothyme
temperament with pyknic physique may possibly be indirect, and due chiefly
to the hypertension associated with excessive weight).