CHAPTER II.

OF THE PECULIARITIES OF ORGANIZATION AND FUNCTION DURING INFANCY AND CHILDHOOD.

AN acquaintance with the physiological condition of the different portions of the body, and the successive and rapid changes which they undergo, in organization and function, from the period of birth until that of puberty, is essential to a correct understanding of the pathology and therapeutics of infancy and childhood. It is to the physiological condition of the several tissues and organs-their successive development and relative activity-that the predisposition to particular forms of morbid action, as well as the various modifications which the phenomena, march, and terminations of disease exhibit, in the earlier stages of existence, is to be attributed; to it, also, reference is to be had in the choice of the therapeutical agents which are employed in their cure.

At the moment when the human being emerges from the womb, and enters upon the enjoyment of a separate state of existence, it presents physiological as well as physical characters, which it preserves during a certain period, altogether distinct from those which are proper to it in the subsequent periods of life. All of the organs are imperfectly developed, while many of them are, as yet, merely rudimental, while the whole of the functions of life are confined, almost exclusively, to those of nutrition. By degrees, however, the different portions of the system become more perfectly organized; the body and limbs increase in size, and exhibit an augmentation of strength and vigor; organ after organ attains successively its full development, and enjoys for a time a predominance of activity; the number and extent of the vital phenomena are thus increased, until, finally, the entire organism is adapted to the active and regular performance of all its functions.

During the whole period of infancy, the activity of the digestive and nutritive functions, the great and rapid change of material which the different organs experience, and the consequent demand for a constant supply of appropriate nourishment, render, under the influence of various disturbing circumstances, errors of nutrition, of frequent occurrence, as also, those diseases which are dependent upon deficient or improper food. The great size and vascularity of the brain, the extreme delicacy and excitability of the skin and mucous membranes, and the great development of the whole lymphatic system, cause these more frequently than other portions of the organism to be the seat of serious and extensive disease; somewhat later their susceptibility to morbid impressions is still more augmented by the process of dentition. The rapid development of the brain,

and the activity of many of its functions, and the simultaneous changes going on in the intestinal mucous membrane, as the teeth make their appearance, render both the intercranial and abdominal organs, at this particular period, especially prone to disease from slight causes.

The excessive nervous excitability of the infant gives to its diseases a peculiar character of mobility-that is to say, morbid irritations occurring in one organ are quickly reflected upon others; and from the great vascularity of every part, especially the abundance of arterial capillaries with which all the organs are supplied, during the progress of rapid growth, sympathetic irritations become very soon converted into organic disease.

While the physiological condition of the several organs, in the stages of infancy and youth, renders them thus prone to take on particular grades of morbid action, it, to a certain extent, also modifies the action upon them of the various remedial agents; nearly all of these acting with increased energy at this period of life, and requiring to be administered in diminished doses, graduated by the particular age of the patient. Some remedies have, likewise, a peculiarity of action different from that produced in the adult, while the action of others is more or less prejudicial. But it is unnecessary in this place, to extend further our remarks on this subject; we shall have frequently to recur to it in subsequent portions of the treatise.

1. Infancy.

The age of infancy extends, agreeably to the division we shall adopt, and which corresponds with that of Müller, from the period of birth to the commencement of the second dentition, or, generally speaking, until the end of the sixth year. According to M. Halle, this period of life includes three distinct physiological epochs; the first, extending from birth to the commencement of the first year; the second, comprehending the period occupied in the process of dentition; and the third, extending to the appearance of the permanent teeth.

Organization. At birth, as already remarked, the entire organism is but imperfectly developed. The body measures from seventeen to twenty-one inches in length, and in weight varies, agreeably to the repeated observations of Professor Chaussier, from six to nine pounds. The skin is of an extreme delicacy, and of a more or less deep red color. It is also more vascular, and more freely supplied with nerves than in after life. At the end of a few weeks, it loses its deep red tint, changing, by degrees, to a dirty yellow, and finally assuming a degree of whiteness which it seldom retains in after life. According to Billard, it is not until towards the end of the third month, that the distinct color of the skin becomes established, so that we can distinguish dark complexioned children from those that are fair. At a much earlier period, the hair has assumed its proper hue, but it is only at the third month that the skin on the body be

comes dark or light-colored, the face either pale or ruddy, and the traits peculiar to each constitution are delineated.

A few days after birth the epidermis commences to exfoliate, and by the fortieth day is usually separated from the whole surface in the form of scales or fine powder. During the entire period of infancy, the skin exhibits great irritability; it is very liberally sup plied also with blood. The articulations retain, for a short time after birth, a semi-flexed condition, and the whole trunk a forward

curvature.

The limbs of the infant are round, smooth, and plump, as well as all the prominent parts on the exterior of the body. This arises from the large amount of fat, and of soft cellular tissue filled with serum, which are interposed between the skin and muscles. As infancy advances the fat diminishes, the cellular tissue becomes more dense, and the exudation into its areola is lessened. The outlines of the muscles are in consequence rendered more apparent, and the form of the limbs and trunk, especially in males, is somewhat changed.

The head and abdomen of the young infant are of a bulk disproportionately large, compared with that of the rest of the body. The pelvis is small and contracted, and the inferior limbs have a much less degree of development than the superior. The median point. of the body is at the umbilicus, or a line or two below it. Several months elapse before the lower limbs acquire a size proportionate to that of the other parts. The thorax is small, flattened at its sides, but somewhat prominent anteriorly. All the tissues abound in lymph, while the lymphatic vessels and glands have a development and activity far superior to what they possess in after life.

In the early period of infancy, the bones are small, red, and deficient in earthy matter, being still, in a great measure, cartilaginous. The central cavity of the long bones can scarcely be said to exist, and the sinuses in those of the head are not at all, or but imperfectly developed. The bones of the skull and the ribs are, however, much more advanced in ossification than those destined for muscular attachment or locomotion.

The muscles are at first soft, pale, and gelatinous; they contain but a small amount of fibrine, and, in common with all the soft parts, are destitute of firmness. They are slender in shape, their fibres are loosely united, the fasciculi not being embraced by fascia or aponeu

roses.

The digestive organs, though less perfectly organized in the early period of infancy than they subsequently become, are, nevertheless, in a condition adapted to produce rapid changes in the aliment introduced into them, and thus to afford a constant supply of materials for the nutrition of the system.

The mouth, with the exception of the teeth, is fully formed, and, by the disposition of the lips and palate, and the obliquity of the posterior nares, is especially adapted for the performance of its proper office of suction.

The mucous membrane, throughout the whole tract of the alimen

tary canal, is thick, soft, and villous-more plentifully covered with mucus, as well as more sensitive and vascular, than in after life. In the stomach, duodenum, and jejunum, it is of a bright rosy tint, but somewhat paler in the ileum and remaining intestines; it often exhibits, on different parts of the surface, large patches of a yellow hue, owing probably to the action of the bile.

When all the liquid parts of the intestinal tube, in early infancy, are removed, there will still remain a layer of thick mucus, adhering closely to the internal surface of the canal, forming on it a kind of plastering. It may be raised by the nail, under the form of a pellicle, resembling, to a superficial observer, portions of the mucous membrane itself. This layer never remains except for a short time; detaching itself by a kind of natural exfoliation. This exfoliation occurs in very thin lamina, which, being rolled together, form the small, white flocculi, so frequently met with in the stools of young infants. When the surface of the duodenum or jejunum is colored with bile, the removal of this layer of mucus removes also the yellow stain. (Billard.)

In the infant, the stomach is much more conical than that of the adult; the entrance of the oesophagus is situated at the left extremity, some distance from the pylorus; the short curvature is also comparatively long, and the large curvature but little developed. It is probably, in consequence of this form of the stomach, that vomiting is so frequent and easy in the infant. The stomach is placed in an almost perpendicular direction, extending from the epigastrium to the umbilicus, in place of transversely, as in the adult. The omentum is peculiarly delicate, and almost entirely devoid of fat.

The small intestines in the infant are nearly one-third longer, in proportion to the length of the whole tract, than in the adult, and the large intestines are longer in proportion to the small, but their calibre is relatively less. The valvulæ conniventes are scarcely ap parent. Separate mucous follicles, about the size of a pin's head, and of a white color, often exist in the jejunum, and in the ileum, follicular plexuses, white and projecting, and often with a slight black point on the top, as in the adult. The cœcum is largely de veloped, and the vermiform process very long. The ileo-cœcal valve slightly projects, while the opening it surrounds is so extremely small, that, in most infants, it would be difficult to pass through it a crow-quill. At this age it prevents the regurgitation. of substances, and even gas, from the large into the small intestines, but allows a free passage for the contents of the small intestines into the large. (Billard.) The depressions and prominences of the coecum and colon are less marked in the infant than in after life. The lacteal vessels, and mesenteric glands, are largely developed.

In the infant the liver has a bulk greatly disproportionate to the residue of the abdominal organs; at birth, filling nearly one-third of the abdominal cavity, descending even to the crest of the ileum. With the change in its circulation, caused by the obliteration of the ductus venosus, and the development of the portal vein, its bulk diminishes, especially on the side of the left lobe.

The gall-bladder is small at birth, but soon enlarges; it contains bile of a green color, but less viscid, and containing less of its peculiar principles, than at a more advanced age.

The spleen is small in size, but presenting no apparent difference from its usual structure in the adult; it can be distinctly felt in the infant, under the short ribs, towards the centre of the abdomen.

The pancreas and kidneys are large; the lobular structure of the latter quickly disappears, and the supra-renal capsules, which are at first of considerable size, rapidly diminish.

The urinary bladder is small, having a more elongated shape than in the adult, and is placed rather above than within the pelvis. The pouch, or fundus of the bladder, is but imperfectly developed, and the cervix is much more dependent than in the adult, which has been assigned as one cause of the frequent discharges of urine, and the difficulty of retaining it during infancy.

The respiratory organs are well developed in the infant. At the period of birth, the cartilages, bones, and muscles of the larynx are perfectly formed; the first two, however, are very small and flexible. The cartilages of the trachea are perfectly distinct from each other, soft, and filled with blood. The mucous membrane of these parts is soft, thick, very vascular, and abundantly supplied with mucus. The dimensions of the larynx and glottis are very small at birth, and remain so during the greater part of childhood, differing but little in size in a child of three or four and one of twelve years. It is this which, in young children, renders all diseases of these parts attended with exudation upon, or tumefaction of, their mucous membrane, so eminently dangerous, because of the complete closure of the glottis which then takes place. The bronchi are perfectly formed, but small, in the infant; they, however, quickly acquire a greater development.

The dimensions of the thorax are proportionably less than those of the other cavities, at birth, and for some time afterwards.

The lungs, which in the foetus were small, dense, and of a brownish color, expand immediately after birth to double their former bulk, becoming soft, crepitant, and of a rosy hue. While their specific gravity is less than in the foetal state, in consequence of the air which pervades their cells, yet their absolute weight, from the greater amount of blood transmitted to them, is doubled."

The chest of the infant upon percussion is very sonorous; chiefly from the thinness of the parietes, and the freedom with which the air permeates the bronchi and the air-cells of the lungs. The thymus gland, which exists at birth, continues to grow for some time after. It remains of considerable size during the first year, after this it usually gradually diminishes in bulk, and, in many instances-but by no means so uniformly as has been generally supposed-it disappears entirely about the period of puberty.

The organs of circulation are fully developed at birth, but during the early period of infancy present several remarkable peculiarities. The volume of the heart is proportionably large; its muscular structure is soft, and of a paler color than in after life, and of nearly