among the latest to come into operation, requiring some assistance from the understanding for their direction and support.

The age of childhood commences with the second dentition, and extends to puberty; including, under ordinary circumstances, in this climate, the period of life between the seventh and fourteenth years. It is the second infancy, according to the division of ages, adopted by M. Halle.

Organization. At the commencement of childhood, the twenty teeth produced by the first dentition, during infancy, become separated from each other, in consequence of the more perfect development of the maxillary bones, and the increased expansion of the dental arches. With the exception of the third molaris in each jaw, they become loose and fall out, their place being supplied by the appearance, during the progress of childhood and youth, of twentysix permanent teeth.

By the enlarged size of the maxillary bones, the face assumes a greater depth and breadth, and the general character of the countenance becomes materially changed. Towards the period of puberty, this change is still further increased, in males, by the appearance, upon the upper lip and chin, of a fine downy hair, which subsequently increases in thickness and coarseness, constituting the beard of the adult.

While the second set of teeth are making their appearance, every part of the body acquires a more perfect development. The lower extremities assume a size and bulk still more in proportion to those of the upper limbs; and the pelvis, especially in females, becomes deeper and more expanded. The bones become still more completely ossified, and those portions of them which, in the infant, were united by cartilage only, are, during this age, consolidated with the body of the bone. The frontal and maxillary sinuses acquire their full development; the joints their permanent forms, and increased firmness; the permanent cartilages assume a greater degree of density, as well as the various aponeuroses and ligamentous bands. The muscles are still small, but fuller, denser, and of greater strength and activity than in infancy. In the male, they have also a greater degree of prominence, in consequence of the continued absorption of the subcutaneous fat, and the increased density of the cellular membrane. This absorption and condensation do not take place to the same extent in the female, in whom, throughout the greater part of life, the limbs, as well as the other external parts of the body, continue, in consequence, fuller, rounder, and more plump than in the male.

The thorax acquires, during childhood, a greater degree of expansion, and the air-cells of the lungs augment in size. The dimensions of the larynx are likewise increased; and towards the period of puberty it presents, in the male, a considerable prominence at the anterior part of the neck; which, however, is more marked in

some subjects than in others. The rima glottidis is also enlarged, and the thyro-arytenoid muscles are elongated.

The organization and development of the brain-particularly of the anterior and superior portions of the cerebrum-are gradually perfected during childhood. About the period of puberty, the cerebellum acquires a very rapid development, being then nearly twice as large, in proportion to the other portions of the brain, as it was at birth. The remaining portions of the nervous system become perfected in organization, and all the organs of sense attain, during childhood, their complete development.

Towards the close of childhood, the organs of generation, in both sexes, are fully evolved, and become covered, externally, with hair. In the female, at this period, the mainmæ begin to appear upon the upper part of the chest.

All the parts of the body preserve, during the earlier stages of childhood, much of the softness of infancy; the predominance of the white fluids, however, gradually diminishes. The various tissues are still liberally supplied with arterial blood, and the capillary system continues more extensively expanded than in after life.

Functions.-The whole of the vital functions proceed rapidly during childhood towards their complete development.

Digestion is still extremely active; almost every species of wholesome aliment is rapidly converted into chyme by the stomach; the appetite is acute, and a frequent and plentiful supply of food is demanded. The sense of hunger is more imperious, and less easily borne at this age, than at any subsequent period of life. Thirst, or a desire for aqueous diluents, is more frequently experienced than during childhood, as well in consequence of the more solid and stimulating character of the food that is eaten, as from the greater waste of the watery portion of the blood, by the active muscular exercise to which the child is prompted by an instinctive impulse. Nutrition is equally active with digestion, assimilation still predominating over decomposition; and hence the body continues to increase in size. The cessation of growth seldom takes place until the twentieth or twenty-first year; and Quetelet has found, from numerous comparative observations, that in the male, the height frequently increases after the above period, even as late as the twenty fifth year; and we have reason to believe, that a regular physiological increase in other organs, especially in different portions of the brain, may occur even beyond this period.

Respiration, although not so frequent as in infancy, is fuller and deeper, in consequence of the greater expansion of the chest; and a larger amount of oxygen is consumed in the process. The action of the heart, though still frequent, is less so than in infancy, and more energetic. The process of calorification has an increased degree of activity, consequently the temperature of the body is higher, and more uniformly maintained, the influence of moderate degrees of cold being borne with greater impunity.

The functions of all the external senses are peculiarly acute, and the intellectual and moral faculties augment daily in extent as well

as in activity. The powers of observing, comparing, judging, of reasoning generally, though still imperfect, have acquired a much greater extent and accuracy. The memory is still quick and tenacious. Hence this period of life is, with great propriety, the one usually devoted to mental education.

Not only is the intellect in childhood more fully expanded, but the higher moral faculties have likewise come into action. The child is capable of distinguishing between right and wrong, virtue and vice, and of understanding, to a certain extent at least, his several duties, whether of a natural, civil, or religious character. He acts less from instinct and feeling, and more from deliberation and judgment, than the infant; nevertheless, he is still, in a great measure, the slave of impulse and of passion.

The expressions and gestures of childhood are strongly marked, and very mutable, betraying the great activity of the mind, and the varied sensations that are experienced in rapid succession. This period of life is noted for great inquisitiveness and extreme loquacity.

Towards the latter period of childhood, articulation has attained a considerable degree of perfection; the voice does not, however, acquire its full depth and compass until subsequent to the period of puberty.

The same desire for constant bodily exertion exists, to a greater extent, even, than in infancy. Confinement of all kinds is endured with difficulty, and, if too long continued, is productive of serious injury to health. Sleep is still profound, and a much greater amount is demanded than in the subsequent periods of life.

As puberty approaches, the genital functions, and the desires connected with them, begin to be developed. The menstrual discharge in females usually commences towards this period.

In the foregoing brief sketch, we have presented the condition of the organization, and of the functions of the human body, at the several stages of development, from infancy to puberty, as it occurs in the generality of cases. Exceptions, however, frequently occur, not only in regard to the period and order of succession in which the march of organization in individual organs takes place, and the activity of their respective functions is displayed, but in the period of growth, and full development of the entire organism.

The number of years that have elapsed since birth does not afford always a positive indication of the physiological condition of the human body, nor of any one of its organs. Climate, moral and phy, sical education, diet, regimen, and various other circumstances, produce so powerful an influence either in retarding or accelerating the development of the whole, or certain parts of the organism, that the same physiological condition of individual organs, or of the entire system, will occur in one individual several weeks, months, or even years, sooner or later than in another. Thus, the age of puberty, especially in females, is attained, in tropical climates, at an age at which, in colder regions, the individual is still scarcely emerged from infancy. In fact, all those circumstances which exert a stimu

lating influence upon the nervous system, or which tend to call early into exercise particular organs, are calculated to produce a rapid and premature development of function, and at the same time, by hurrying the organism through the various stages of organization, impair its energies, and abridge the period of its existence. While, on the other hand, everything calculated to abstract the organs of the body from the full influence of the natural stimuli-to retard their exercise or impair their nutrition, will protract the period of their development, or even prevent their complete organization. Thus, in warm climates, the stage of infancy is extremely short, that of puberty is early attained-the period of maturity arrives and passes with equal rapidity, and the decrepitude of old age is experienced, often, when, in colder climates, the body is still in the enjoyment of all its vigor. A soft and luxurious life, heating aliments and drinks, deprivation of muscular exercise, premature exercise of the intellectual organs, or early excitement of the passions, exert a somewhat similar influence. On the other hand, in cold climates, and by deficient or unnutritious food, the want of proper moral and intellectual culture, and other depressing causes, the development of the body is retarded, and its complete organization, with the full and vigorous exercise of its functions, if attained at all, is attained only by slow degrees, and at a late period.

From a variety of causes, to which the child is subjected from birth, or during the period of infancy or childhood, a single organ, or system of organs, acquires a degree of development beyond that of the rest, and causes the functions performed by it to assume a very evident predominance. Thus, in some children, the head is large, and great activity and intelligence are early displayed; in such, the cerebro-spinal system has acquired a predominance of development and function, constituting the nervous temperament. In other children, great muscular power is early displayed; the chest is capacious; the various parts of the body well nourished, and the complexion florid; the circulatory system, and the organs engaged in hæmatosis and nutrition, predominate; there are considerable strength and activity of body, with, in general, moderate intellectual activity or power. This constitutes the sanguineous

temperament.

A prominent abdomen, with a languid circulation, and paleness of the skin, a craving appetite, and but little activity either of mind or body, indicate the predominance of the abdominal organs and lymphatic system, and constitute the marks of the lymphatic temperament.

"The expression of the countenance, or form of the features, is also," remarks Evanson, "some indication of the prevailing temperament. Thus, the development of the forehead indicates the proportion of the encephalon: the part between the forehead and mouth is, in general, in harmony with the development of the thorax, while the lower part of the face is in relation to the size of the abdomen; so that in each we have an index of the temperament, whether cra nial (nervous), thoracic (sanguineous), or abdominal (lymphatic)."

Other varieties of temperament occur, and some individuals present no strongly-marked temperament-the development of the several organs being nearly equal; or, on the other hand, more than one of the above temperaments may occur in the same individual. In infancy and childhood, the lymphatic temperament has a tendency to prevail. The nervous becomes more particularly manifest at or after the age of seven, when, as we have seen, the brain attains a more full development, while the sanguineous belongs, more properly, to a later period, when the thoracic organs acquire their proper organization and fulness of function.

The particular temperament of the individual may be born with him, and in many cases is hereditary; or it may be developed during infancy and childhood by the influence of the external agents to which the child is subjected, or by errors in his physical and moral treatment. The leading principle upon which the treatment of children should be invariably conducted, is to allow to every organ its equal and appropriate nutriment; and while no one is forced into activity prematurely, to give to each its equal and appropriate share of exercise-promoting the development, at the proper season, of those which are deficient in activity, and removing every unnecessary stimulant from such as exhibit a tendency to a disproportionate development and activity of function.

CHAPTER III.

PATHOLOGY OF INFANCY AND CHILDHOOD.

DURING infancy and childhood there exists a very strong predis-. position to disease. This predisposition is the greatest within the first year subsequent to birth, and it gradually decreases with the increase in the age of the child. During the first few weeks of existence, the imperfect organization of every part of the body, and the deficiency in vigor of most of its functions, render it peculiarly liable to the action of various agents, the impression of which, while it may be sustained with comparative impunity at a later period, produces, in the delicate organs of the infant, the most serious disturbance, resulting, in the greater number of cases, in a rapid extinction of life. At birth, and for a short time subsequently, the vital powers are, in fact, so feeble, that they present but little resistance to the agents by which they are assailed, but sink rapidly under their influence. Even when the infant has become endued with greater tenacity of life, the predominant activity of the ganglionic system, and of the nutritive function, and the extent of the capillaries

During the ten years preceding 1845, 1145 children under one year of age died in Philadelphia from debility alone.