Physiology: The Science of the Body

by Ernest G. Martin

The connections between muscles and nerves are also pretty well established at the time of birth, so that the body and limbs can be moved freely, even if not at all efficiently.

Not only are the motor nerves formed and in connection with the muscles at and even before birth, but the sensory nerves and most of the central nervous system are ready to begin functioning as well. Some reflex actions, including a few that require quite elaborate muscular and nervous coordination, are performed very shortly after birth. One famous example, that has been much cited as tending to reinforce the belief in man’s descent from tree-dwelling ancestors, is the curling of the fingers about a slender rod that is pressed against the palms. In most very tiny babies the grasp thus secured is strong enough so that the child can be raised and held in the air, supported wholly by its own grip. Sneezing, which is really a very complex act, requiring accurate cooperation on the part of many muscles, is done successfully by very young infants. The reflex of sucking, which is of paramount importance, in that without it the child would almost inevitably starve, is present practically from birth. Another important early reflex is that of crying. It is a curious thought that this reflex, by which bodily discomfort is made known, and through which relief may be summoned, is revealed at the very instant of birth, in connection with the drawing of the first breath, while the contrary reflex of laughter, by which bodily well-being is expressed, puts in an appearance only after some weeks or even months.

It is difficult to determine just how far the sense organs have arrived in their development at the time when the infant begins its independent existence. That touch and those senses related to bodily discomfort, of which pain is most important, are operative from the first is shown by the occurrence of the reflexes described above, which are brought into action by those particular senses. There is good reason to believe that the sense of hunger comes into play within two or three days at the latest. The sense of thirst does not have much chance to reveal itself early in life, for with a diet exclusively liquid, and feedings separated by only a few hours, there is no reason why the child should become thirsty. As the feedings become less frequent, and particularly as solid food begins to be added, there is real danger that the child may be insufficiently supplied with water.

Muscle sense and the equilibrium sense, if present at all, must be in a very imperfect condition at first. They seem to differ from the senses described thus far in that they depend on practice for their development. At any rate the bodily movements are largely aimless in the beginning, and it will be observed that the baby has the appearance of experimenting with its extremities, placing them repeatedly in particular positions and seeming to gain precision thereby. The eye movements, and especially those by which both eyes are focused on a single object, depend for their accuracy on the working of muscle sense. In the estimation of the parents a distinct mark of progress is registered the first time the baby follows a movement with its eyes. As soon as it does this accurately, and also brings both eyes to bear on any object, its muscle sense is known to be in efficient operation, so far, at least, as the eye muscles are concerned. Equilibrium sense first shows itself when real balancing motions of the body are made.

The senses of taste and smell may be operative to some degree in very young children, but it is doubtful whether they have either the breadth or the acuteness that will be shown later in life. Recognition of disagreeable tastes or smells seems to appear earlier than appreciation of agreeable. This is in line with the general fact that the self-protective reactions are developed very early.

Hearing and sight are probably in working order practically from birth. It is customary to test the sight of the new-born by passing a light directly in front of the eyes. If sight is present there will be some appreciable eye movement, suggesting that the eyes are attempting to follow the moving light. There is no reason to believe that there is any such thing as definite looking at objects thus early. So long as the eyes continue to roll aimlessly about, and before they begin to focus accurately, they are more likely concerned with distinctions between light and shadow, than with perceptions of form or size. In general we may say of the senses that those concerned immediately with bodily discomfort are about as fully developed at birth, or shortly thereafter, as they ever will be, while those that have to do with the general adjustments of the body to its environment reach full efficiency more gradually.

The higher parts of the brain, especially those concerned on the one hand with the mental life (the cerebrum), and on the other with the complicated reflex acts involved in locomotion (the cerebellum), are not ready to begin active functioning when the child is born. Indeed some parts of the cerebellum do not take on final form for from eight months to two years afterward. It is thought by some that the question of whether a child will learn to walk early or late depends, in part at least, on how soon his cerebellum reaches complete development.

Most parents are fully alive to the importance of abundant warm covering when their children are to be taken out into the cold, but there is much less appreciation of the harm that may be done by too much clothing in extremely hot weather. Of special importance is the avoidance of exposure to sharp drops in temperature. The adult adjusts himself more or less automatically to these, whereas the infant does so to only a limited extent.

Finally, the hold of the infant upon life, that quality that we know as ruggedness or vitality, is much slighter than it will be after a few years. Not only is the susceptibility to many kinds of infectious diseases very much greater, and the power of resisting them very much less, but the ill effects of poisons, whether taken in with the food or breathed in with the air, are more pronounced. Thus the vitiated air of slum dwellings, saturated with the effluvium from unwashed bodies and unclean clothing, while trying enough for the average grown person, is deadly for all but the toughest babies. Even in the ordinarily well-kept home, especially in the winter time when ventilation is apt to be neglected, the air within the house tends to become unsatisfactory from the standpoint of the infant’s welfare.

The wise parent, and wise he must be at this time, relaxes his care in just proportion as the child achieves ability to do things for himself. Since bodily development is more rapid than mental the close supervision of food, clothing, and physical occupation is necessary only during the early years, but the task of building up, through the slow processes of education, the sort of mind which will be able to do its proper share in dealing with the difficulties which confront the coming generations is one to which may well be devoted the best thought and effort not only of the parents, but of organized society as a whole.