DEVELOPMENT AFTEK BIRTH, AGES, AND DEATH. 945 



tion offered was the fact that the arteries going to the left side are usually larger than 

 those on the right. There were no observations with regard to the comparative size of 

 the arteries upon the two sides in left-handed persons. 



Eeasoning from the facts just stated, Dr. Ogle conceives that dextral preeminence 

 depends upon a natural predominance of the left side of the brain, the reverse obtaining 

 in the left-handed. This view seems to afford the most rational explanation of dextral 

 preeminence. It is generally true that the members on the right side are stronger than 

 the left, particularly the arm ; but this is not always the case, even in the right-handed. 

 A not inconsiderable practical experience in athletic exercises has led us to observe that 

 the right hand is more conveniently and easily used than the left, from which fact we 

 derive the term dexterity; but that the left arm is often stronger than the right. In 

 many feats of strength, the left arm appears less powerful than the right, because we 

 have less command over the muscles. As a single illustration of this, we may mention 

 the feat of drawing the body up with one arm, which requires unusual strength, but very 

 little dexterity. In a number of right-handed persons, we find many who perform this 

 feat more easily with the left arm, and not a few who can accomplish it with the left 

 arm and not with the right. When we come to the cause of the superior development 

 of the left side of the brain, we must confess that the anatomical explanation is not 

 entirely satisfactory. We can only say that the two sides of the brain are generally not 

 exactly equal in their development, the left side being usually superior to the right, and 

 that we ordinarily use the muscles of the right side of the body in preference to those 

 of the left side. 



.Development after Birth^ Ages, and Death. 



When the child is born, the organs of special sense and the intelligence are dull ; 

 there is then very little muscular power; and the new being, for several weeks, does lit- 

 tle more than eat and sleep. The natural food at this time is the milk of the mother, and 

 the digestive fluids do not, for some time, possess the varied solvent properties that we 

 find in the adult, though observations upon the secretions of the infant are few and 

 rather unsatisfactory. The full activity of pulmonary respiration is gradually and slowly 

 established. Young animals appropriate a comparatively small quantity of oxygen, and, 

 just after birth, they present a much greater power of resistance to asphyxia than the adult. 

 The power of maintaining the animal temperature is also much less in the newly-born. 

 The process of ossification, development of the teeth, etc., have already been considered. 

 The hairs are shed and replaced by a new growth a short time after birth. The fonta- 

 nelles gradually diminish in size after birth, and they are completely closed at the age of 

 about four years. 



The period of life which dates from birth to the age of two years is called infancy 

 At the age of two years, the transition takes place from infancy to childhood. The 

 child is now able to walk without assistance, the food is more varied, and the digestive 

 operations are more complex. The special senses' and the intelligence become more 

 acute, and the being begins to learn how to express ideas in language. The child gradu- 

 ally develops, and the milk-teeth are replaced by the permanent teeth. At puberty, 

 which begins at from the fourteenth to the seventeenth year a little earlier in the 

 female the development of the generative organs is attended with important physical 

 and moral changes. 



The different ages recognized by the older writers were as follows : Infancy, from 

 birth to" the age of five years ; adolescence, or youth, to the twenty-fifth year ; adult 

 age, to the thirty-fifth year ; middle life, to the fiftieth year ; old age, to the sixtieth 

 yeaf ; and then, extreme old age. A man may be regarded at his maximum of intellect- 

 ual and physical development at about the age of thirty-five, and he begins to decline 

 after the sixtieth year, although such a rule, as regards intellectual vigor, would cer- 

 tainly meet with numerous exceptions. 

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