160 SECTIONAL ADDRESSES 
way they have been treated by the outside world in various situations and 
the like. 
(3) About 44 per cent. reported experiences from their own intro- 
spections—it might be some intellectual change in reaction such as the 
emergence of old recollections, or it might be an affective change such as a 
disinclination for amusements. 
Important is the fact that bodily and mental manifestations certainly do 
not go together and have widely different values for different individuals. 
Some lay great stress on bodily signs and hardly any on the mental, while 
others do just the reverse. It is not, of course, suggested that the per- 
centages reported above would agree with medical diagnosis, as the 
subjects belonged to a sample of the general population. Moreover, 
many of the physical symptoms reported had probably a mental origin, 
for, as Prof. M. Greenwood stated in a recent lecture on ‘ The 
Temperamental Factor in Industry,’ ‘ it is becoming realised more and 
more how easily emotional disturbances may result in bodily ills that 
can be cured only by dealing with their psychological causes.’ 
Before referring to some systematic experiments with adult subjects 
it may be useful to account for the fact that this is largely a new develop- 
ment. Child psychology has largely occupied the attention of psycho- 
logists during the last thirty years. The educational and vocational 
implications were so obvious and tremendous that it was only fitting 
that ‘ Children first’ should virtually be the slogan. But it is equally 
clear that the study of children is in many respects less difficult than 
that of adults. t 
(x) Adult populations are relatively inaccessible. 
(2) There are formidable statistical difficulties relating to the selection 
of samples. 
(3) The widely different kinds of experience and mental backgrounds 
of adults make it difficult to differentiate between what is largely native 
and what is largely acquired. 
(4) Care must be taken, on the one hand, that tests do not unduly 
favour the adult by involving his greater retention of some kinds of know- 
ledge and acquired skill, or, on the other hand, do not unduly handicap 
him owing to his lack of practice in activities similar to those demanded 
by the tests, or by virtue of changes in his attitude towards testing or 
through his having formed habits which do not conduce to high scoring. 
Children have probably greater incentives to put maximum effort and in 
many cases they have probably enjoyed superior schooling. 
(5) There is the danger of assuming that conclusions drawn in child 
psychology hold also for adults. Thus the relation of speed to power 
may be different for adults. 
(6) Finally, the rate of growth (or of deterioration) is generally slow 
in maturity. During childhood it is easy to distinguish between the — 
general mental capacity of two average children differing in chronological 
age by only one year, but who would care to differentiate between the 
average youth of twenty and the average man of forty? For biologically 
senescence depends on the increase of protoplasm and on the differentia- 
tion of cells. ‘Thus the rate of growth depends on the degree of senescence, 
