278 PHYSIOLOGY CHAP. 



either to the slight and imperfect morphological differentiation or 

 to the constitution of its chemical components. Cohn (1907) says 

 that during the first year of life the development of the brain is 

 carried on at the cost of protein substances, whereas the 

 constituents containing phosphorus diminish slightly, and the 

 quantity of calcium contained in the cerebral substance is notably 

 less, more particularly during the last period of foetal life and the 

 first months of extra-uterine life. Tetany during childhood is, 

 according to Quest, associated with an abnormal lack of calcium 

 in the cerebral matter. 



The sense of touch, temperature, and pain are well developed in 

 the new-born infant ; this is also the case with taste and perhaps 

 also with smell. The pupil is larger than in the adult. The 

 infant born at full term shows a distinct movement in response to 

 light, although central vision is not as yet established and several 

 weeks must elapse before the infant's eyes are capable of looking 

 steadily at any object. Magitot (1909) noticed the above- 

 mentioned reflex in children born prematurely, a proof that the 

 optic nerve is capable of transmitting the stimulus to the centres 

 even before its fibres have been provided with their medullary 

 sheath. 



The auditory sensations in the new-born infant are extremely 

 dull and confused ; this is due to the fact that the middle ear is 

 stopped up with an amorphous gelatinous substance, which fits 

 into all the crevices of the tympanic cavity and disappears with 

 the first breaths (Gelle", Giovanardi, Wreden). The cavity of the 

 tympanum is therefore purely potential at the moment of birth, 

 and is first formed when the respiratory movements facilitate the 

 absorption of the lymph which renders turgid tlio sub-mucous 

 membrane lining the tympanum. The mucous surfaces recede 

 from one another, thus making pervious the hollow of the middle 

 ear which is filled with air by the Eustachian tube ; when this 

 cavity is sufficiently large, the membrane of the tympanum is 

 able to vibrate and to transmit the vibrations to the fenestra 

 ovalis by means of the chain of ossicles. Hence the new-born 

 child is deaf and only acquires the sense of hearing gradually after 

 five or six days of life (Preyer, Poli). Thus sensations are 

 developed gradually by successive experiences. 



III. The age of childhood is, in the strictest sense, the period 

 of growth. It is true that during intra-uterine life, adolescence, 

 and youth the individual increases both in size and weight, but 

 foetal life is more especially the period of the creation of tissues 

 and organs, whilst in adolescence growth is somewhat less marked 

 than in infancy and is subject to interruptions. During childhood, 

 on the other hand, growth is progressive ; it is most rapid during 

 the first stage of infancy and gradually diminishes during the 

 successive stages of childhood. If we estimate the differences 



