DEVELOPMENT 453 



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moreover, how to use his senses to the best advantage. Hence the effec- 

 tive result of sensation in general in childhood is far below that of the 

 adult, although the latter's actual sense-organs may be less perfect as 

 mechanical instruments than are those of the child. (See the preceding 

 chapter.) 



More marked, even, than the bodily characters of childhood are those 

 of the Mental Aspects of the individual when young. Into these, so 

 amply discussed are they in pedagogical and psychological literature 

 (e. g., by Stanley Hall), we cannot go here. Three principles, however, 

 may be mentioned which are more or less important in medicine. First, 

 the young child lacks mostly whatever degree of voluntary control over 

 the physiological and reparative processes the adult mind exerts. This 

 makes the child a more passive and more plastic patient as well as pupil. 

 Its physiology is perhaps to be found in the incomplete command over 

 the so-called "voluntary" musculature which is so conspicuous an aspect 

 of childhood. How far this control extends over the vegetative func- 

 tions in the clever and accomplished adult we do not a's yet commonly 

 appreciate. 



The child is relatively nai've and open to all kinds of influences. Habit 

 in this period of life has not yet laid its all-encircling and resistless fingers 

 on both the body and the mind. Children therefore are more amenable 

 to all sorts of therapeutic and hygienic measures, and especially 'to those 

 which, like suggestion, do their work through the mental processes. 



Worry has not yet fixed its hold on the normally cared-for child. In 

 the adult this is a source of harm whose importance it would be hard 

 indeed to exaggerate. Chronic emotion of fear as worry is, its asthenic 

 effects on bodily processes are certain, and none the less so because the 

 mode of its action is not fully made out. It is hard not to believe, as has 

 been suggested, however, that worry through the trophic nerve-impulses 

 depresses the metabolism and so undermines the resistance of many 

 kinds of tissue. Working in the opposite direction of invigoration and 

 stimulation, joy and happiness exert a wholly beneficial effect on the 

 vital. functions. Childhood, normally the joyful age in our perhaps too 

 strenuous civilized life, receives the full benefit of this continual sthenic 

 influence. Not a little of the versatile freshness of the child's bodily 

 metabolism may come from this sort of mental stimulation as it may 

 come to all humanity centuries hence, when the old-time worries, largely 

 based on the struggle for existence and good health, may be outgrown. 



Maturity or adulthood is the general subject-matter of ordinary 

 physiology and needs here no separate discussion. So far as the general 

 activities of life most useful to the world's evolution are concerned, it is 

 preeminently the period of achievement. It is," for example, the period 

 of reproduction, biologically one of basal life-functions. It is the epoch 

 of the bodily strength which in the childhood before it has been devel- 

 oping and which in the senescence after it will gradually lessen again. 

 This gradual accumulation of experience, wisdom, etc., during the period 

 of maturity changes the nature or quality of the individual's capacity, 



