CHAP, v.] THE PHASES OF LIFE. 687 



increases up to the second year, and may then remain for a while 

 stationary, but generally before puberty, has suffered a retro- 

 gressive metamorphosis, and frequently hardly a vestige of it 

 remains behind. The thyroid body is also relatively greater 

 in the babe than in the adult; the spleen, on the other 

 hand, which grows rapidly in early infancy, is not only absolutely, 

 but also relatively, greater in the adult. It need hardly be 

 said that the recuperative power of infancy and early youth is 

 very marked. 



It would be beyond the scope of this work to enter into the 

 psychical condition of the babe or the child, and our knowledge 

 of the details of the working of the nervous system in infancy 

 is too meagre to permit of any profitable discussion. It is hardly 

 of use to say that in the young the whole nervous system is 

 more irritable or more excitable than in later years ; by which 

 we probably to a great extent mean that it is less rigid, less 

 marked out into what, in preceding portions of this work, we 

 have spoken of as nervous mechanisms. It may be mentioned 

 that stimulation of the various cerebral areas, in new-born animals, 

 does not give rise to the usual localized movements. The sense 

 of touch, both as regards pressure and temperature, appears 

 well developed in the infant, as does also the sense of taste, 

 and possibly, though this is disputed, that of smell. The pupil 

 (larger in the infant than in the man) acts fully, and Bonders 

 observed normal binocular movements of the eyes in an infant 

 less than an hour old. The eye is (in man) from the outset 

 fully sensitive to light, though of course visual perceptions are 

 imperfect. As regards hearing, on the other hand, very little 

 reaction follows upon sounds, i.e. auditory sensations seem to be 

 dull during the first few days of life ; this may be partly at least 

 due to absence of air from the tympanum and a tumid condition 

 of the tympanic mucous membrane. As the child grows up his 

 senses rapidly culminate, and in his early years he possesses a 

 general acuteness of sight, hearing, and touch, which frequently 

 becomes blunted as his psychical life becomes fuller. Children 

 however are said to be less apt at distinguishing colours than in 

 sighting objects ; but it does not appear whether this arises from 

 a want of perceptive discrimination or from their being actually 

 less sensitive to variations in hue. A characteristic of the nervous 

 system in childhood, the result probably of the more active meta- 

 bolism of the body, is the necessity for long or frequent and deep 

 slumber. 



Dentition marks the first epoch of the new life. At about seven 

 months the two central incisors of the lower jaw make their way 

 through the gum, followed immediately by the corresponding teeth 

 in the upper jaw. The lateral incisors, first of the lower and then 

 of the upper jaw, appear at about the ninth month, the first molars 

 at about the twelfth month, the canines at about a year and a half, 



