INFANCY. 1019 



trcmity of femur; white and gray substances of brain become distinct ; liver de- 

 scends* to umbilicus; testes have passed inguinal ring, and are frequently found 

 in the scrotum; meconium at termination of large intestine; middle point of body 

 at umbilicus, or a little below it. 



865. From the time of its entrance into the world, the condition of the 

 Human infant is essentially changed. It is no longer supplied with nutri- 

 ment by the direct transmission of organizable materials from the circulat- 

 ing fluid of the mother to its own ; but obtains it by the processes of diges- 

 tion, absorption, and assimilation, which involve the establishment of new 

 modes of vital activity in its own organism. In order, however, that the 

 change may not be too sudden, the nutriment provided by Nature for the 

 early period of infantile life, is such as to occasion the least possible demand 

 upon its vital powers for the preparation of the organizable material which 

 is required for its further growth and development. But the transition is a 

 most important one in another particular ; the infant is now thrown in a 

 great degree upon its own resources for the generation of its Heat ; and this 

 it is enabled to accomplish by the combustion of a portion of its food, which 

 is specially provided for the purpose, this combustion being promoted by the 

 arrangements for that active Respiration, which now supersedes the very 

 limited aeration of its circulating fluids that was sufficient during foetal life. 

 In the movements of the respiratory muscles and of the walls of the ali- 

 mentary canal, we have a new source of expenditure of vital force, and of 

 destruction of tissue; and this expenditure is progressively augmented as 

 the motions of the body and limbs become increasingly active. Thus we 

 find that the formative powers are not exercised during Infancy and Child- 

 hood, solely in the construction and augmentation of the fabric (as they were 

 during embryonic life), since there is a constant demand upon them for its 

 maintenance; and this demand becomes greater and greater, in proportion 

 to the activity of the Animal powers. These, at first called into exercise by 

 the stimulus of sensory impressions upon the Nervous system, are speedily 

 brought into very energetic operation. This operation is of an extremely 

 limited character, being at first purely sensorial, and for some time after- 

 wards simply perceptive. But the whole Mind (such as it is) being given up 

 to it, habits of observation are formed, which are never subsequently lost ; the 

 infant learns how to use his Organs of Sense ; and he also acquires those 

 powers of interpreting their indications, which become so completely ingrafted 

 into his nature, as henceforth to seem a part of it. Although this Education 

 of the Senses will necessarily go on, even without any intentional assistance 

 on the part of others, yet it is in the power of the Mother or Nurse to pro- 

 mote it effectually, by supplying objects of various kinds which the Infant 

 may look at and grasp, and' by not abruptly interfering (by the too speedy 

 withdrawal of such objects) with the process by which the visual and tactile 

 perceptions are blended and harmonized ( 619). The Nervous system of 

 the Infant, although thus called into extraordinarily energetic activity, can- 

 not long sustain that activity ; a very large measure of Sleep is required for 

 the restoration of its speedily exhausted powers, and any unusual excite- 

 ment of them tends to injurious disturbances of its nutrition. It is owing 

 to this peculiar susceptibility of the Nervous system of the infant to external 

 influences, that medicines (especially narcotics) which exert a special influ- 

 ence upon that system, are so peculiarly potent in their effects at this period 

 of life, that the greatest caution is needed in their administration. 



866. The most important developmental change which occurs in Infancy, 

 after the complete establishment of the extrauterine circulation ( 783), is 

 the completion and eruption of the first set of teeth ; the greater part of 

 whose formation, however, has taken place before birth. These "milk" or 



