PHYSIOLOGIC AND PSYCHOLOGIC PECULIARITIES The distinct features just described in connection with the mor phology, of the child's nervous system let it at once be supposed that its function, likewise, is still imperfect and atypical. Indeed this fact already becomes manifest on examination of the peripheral nervous system. The excitability- both of motor nerves and of niuscles, tested by means of faradic and galvanic electricity, is decidedly faint until about the eighth week; the muscular response is sluggish (C. Westphal, Soltmann, A. Westphal). Altogether by degrees the characteristic features of the adult response become well-defined, and then only after a long phase of hyper-excitability (the so-called spasmophile period), which, by S0711C, is regarded as normal, but which Mann more correctly considers pathologic, and the indication of a widespread thseased state, however insignificant in its intensity. The sensory nerves also show but slight sensitiveness to electricity for some little time after birth; in the newborn, the face itself is totally insensitive to even strong electric currents.
The very considerable and even uncommonly marked variations in the frequency and regularity of the heart's action, the changeable quality of the pulse, the frequency with which respiration, likewise, assumes an intermittent or arrhythmic type; show that there is no equilibrium between the exciting and inhibitory powers of the nerve centre during the first week of life. The defective inhibitory pow-er of the vagus has been experimentally demonstrated in animals, by Solt mann. That the inciting and regulating influences of the brain, and more particularly of the cerebrum, should still be imperfect at birth, is readily conceivable, if it be borne in mind that considerable areas of the brain receive their myelin only at a later and very variable period of infancy. Then, while the function of nerve fibres may not be entirely dependent upon the presence of the myelin element., its absence must nevertheless limit their conducting power to a considerable extent. and smiously compromise the physiologic accomplishments of all ner vous funetion. 'We know, not alone from the actual evidence which pathology affords, but also from the results of animal experimentation and neurologic examination of the newborn, that destruction of myelin is followed by disturbances of greater or lesser intensity. In animals (cats, dogs, etc.) blind at birth, the closure of one eye delays the appear ance of myelin in the corresponding optic nerve (Held). The optic nerve of a child born at the eighth month, shows, a month later, a much greater proportion of myelin than that of a child born at term (Flech sig). The spinal cord, the cerebral centres and nerve tracts which govern the first (reflex) external manifestations (fcetal movements) of Efe, and in the newborn, vegetative growth, the acts of sucking and tasting, and soon, the instinctive recognition of food, etc., are the first to receive their myelin constituent, as was previously stated. The fact that at birth, extensive areas of the brain are devoid of myelin, certainly affords a plausible explanation of the absence, or at least inadequacy, of its function.
The brain of newborn animals reacts differently to electrical stim ulation from that of the fully grown. The irritation of both motor and sensory centres produces an entirely different effect (Steiner).
Then, in the greater necessity for sleep (about 20 hours a day duting tbe first weeks, 13-t5 hours by the end of the first year), we have a good criterion of the peculiar structural character and func tional inadequacy of the child's central nervous organs. From the standpoint of hy-giene of the nervous system in infancy and early,- child hood, it cannot be too often repeated, that during the first months of lifc, not only every- strong and shrill or glaring (acoustic, optic, ete,) impression, but also any irritation of milder degree, if uniform in inten sity- and long continued, wears out, indeed exhausts, the brain. Again, when as a consequence of certain, and by no means infrequent, irreg ularities in development, special aptitudes become manifest at an unusually early age, is it tnost undesirable to further develop and cul tivate them; almost invariably- does such effort prove detrimental to the general condition of the nervous system. An interesting insight into the functional inadequacy and peculiarity of the child's nervous system may also be obtained by testing the reflexes. The tendon reflexes, the knee jerks more particularly, are already appreciable in the premature infant; from the second month to the second year they are distinctly livelier than in healthy adults. With the exception of the first week of extra-uterine life, when it is more often absent, the abdominal cutaneous reflex is likenise most active in infancy; the same may be said of the plantar reflex. A striking peculiarily in this connection, is the presence, until from the sixth to the tenth month, of the Babinski reflex; a phenomenon of pathologic significance in the adult, but which, at this period of imperfect cerebral function, repre sents the normal reaction. Oppenheirn's reflex (Unterschenkelpha nomen) may likenise be elicited in healthy infants. The reflex closure of the eyelids on the approaching of a finger, occurs already at birth, is particularly active during the first month and often has a dorms-like character. Winking, on the other hand, which is a true optic reflex, does not occur in the newborn and is rarely observed before the sixth to the eighth week. The pupillary reflex to light, which is already appreciable in the prematurely born, shows particular activity and amplitude (more especially in girls) in the latter phase of infancy. A distinct reaction to accommodation the author has only- obtained after the fourth week. The very fine oscillations of the pupil (Psycho reflexe), which, as is well known, are almost constantly perceptible and represent the reaction determined in the organism by the con stantly varying psychic and sensory impressions (Rieger, von Forster, Laqueur, etc.), become manifest in children (individual precocity occa sionally presenting) only after the third month.