DEVELOPMENT 451 



commissary organs are able not only to replace the protoplasm worn out 

 by the intense youthful activities, but to do more to cause the rapid 

 growth of the body. As we have just seen, this causes a doubling of the 

 body-weight between seven and fourteen years. The child's digestive 

 system, like all his others, is more plastic and more adaptable than the 

 adult's, for it has not as yet become habituated to certain ruts in part of 

 mental origin but always in the nature of defect, such as most grown-up 

 persons fall into. 



Muscular action in childhood is more lively but inherently less accu- 

 rate than that of the adult. The ultimate usefulness of youth lies in its 

 ability to elaborate the neuro-muscular mechanism into the wonderful 

 perfection seen in the capable and clever adult. All know how vastly 

 complex is this machine, and how countless its coordinations and its 

 combinations of movement. In the infant up to four months or so 

 voluntary movements are of no immediate use at all, for they are so much 

 at random and so grossly inexact as to be only general tendencies of action 

 toward some object or end. From this, the merely formative stage of 

 neuronal inter-knitting, up to the expertness of the clever craftsman or 

 performer in a thousand different ways, the development is in the direction 

 of the acquirement of better and ever better and more numerous coordina- 

 tions and neuromuscular adjustments. For this the new individual 

 was created. 



The circulation during childhood differs from that in adult life chiefly 

 in its irregularity and variability. Especially is this so in girls and 

 during the first six or eight years. This is due to several causes, among 

 which are the greater elasticity and variability of the tissues, particularly 

 the blood-vessels; the incomplete development of the circulation-regu- 

 lating nerve-centers; and the greater irritability of the nerves. There 

 is often a better-marked dicrotism in the pulse of a child than can be 

 found in adults, due doubtless to a greater elasticity of the arterioles. 

 The pulse-rate appears to lessen from its beginning early in fetal life (up 

 to about seventy years, when it increases slightly), and to be always faster 

 in females than in males. As was said above, in the fetus it is from 160 

 down to 110 or so; atone year it is about 110; at four years, 100; at eight 

 years, 85; four years later, 80; and in adult years from 70 to 80. For 

 girls the rates are considerably higher. According to Vierordt the 

 circulation-time at birth is twelve seconds, while recent research has 

 shown the time required in the adult to be about forty seconds. There 

 is little satisfaction to be had clinically in the child's pulse, because it is 

 so variable a process even in perfect health, especially up to the ninth 

 or tenth year. 



Owing to the more active muscular life and metabolism of the child, 

 his lymph-flow is livelier than that of adults, and the vital process is 

 correspondingly strong while the lymph-glands and the lymph-vessels are 

 relatively larger. Digestion, especially of fats, is relatively better in 

 childhood, and the lymph takes an important part in the process and in 

 nutrition in general. 



