1020 CHARACTERISTICS OF DIFFERENT AGES. 



"deciduous" teeth, 20 in number, usually make their appearance in the 

 following order: The four central Incisors first present themselves, usually 

 about the 7th month after birth, but frequently much earlier or later; those 

 of the lower jaw appear first. The lateral Incisors next show themselves, 

 those of the lower jaw coming through before those of the upper ; they 

 usually make their appearance between the 7th and 10th months. After a 

 short interval, the anterior Molars present themselves, generally soon after 

 the termination of the 12th month; and these are followed by the Canines, 

 which usually protrude themselves between the 14th and 20th months. The 

 posterior Molars are the last, and the most uncertain in regard to their time 

 of appearance; this varying from the 18th to the 36th mouth. In regard 

 to all except the front teeth, there is no settled rule as to the priority of ap- 

 pearance of those in the upper or under jaw ; sometimes one precedes, and 

 sometimes the other ; but in general it may be stated, that whenever one 

 makes its appearance the other cannot be far off. The same holds good iu 

 regard to the two sides, in which development does not always proceed 

 exactly pari jjassu. The period of Dentition is sometimes one of consider- 

 able risk to the Infant's life, and this especially when an irritable state of 

 the nervous system has been brought about by unsuitable food, unwholesome 

 air, or some other cause of disordered health. In such cases the pressure 

 upon the nerves of the gum, which necessarily precedes the opening of the 

 sac and the eruption of the tooth, is a fruitful source of irritation ; producing 

 disturbance of the whole system, and giving origin to Convulsive affections 

 which are not unfrequeutly fatal. These have been particularly studied by 

 Dr. M. Hall, who recommends the free use of the gum-lancet, as a most im- 

 portant means of prevention and cure ; but the Author has no doubt that 

 too much attention has been given to the immediate source of the irritation, 

 and too little to the general state of the system ; and that constitutional 

 treatment, especially change of air, and improvement of the diet, is of fun- 

 damental importance. In infants whose general health is good, and who are 

 not overfed, Dentition is usually a source of but very trifling disturbance ; 

 a slight febrile action, lasting only for a day or two, being all that marks 

 the passage of the tooth through the capsule, and its eruption through the 

 gum taking place without the least indication of suffering or disorder. Any 

 existing malady or abnormal tendency, however, is pretty sure to be aggra- 

 vated during the " cutting of the teeth ;" and it is therefore of the greatest 

 consequence that the infant should be withdrawn during this period from all 

 injurious influences; and that no irregularity of diet, or deficiency of fresh 

 air and exercise, should operate to its disadvantage. 



<S(>7. Although there are no well-marked divisions between the periods of 

 Childhood, Youth, and Adolescence, through all of which we witness the 

 continuance of the processes of Growth and Development (though in a 

 gradually-decreasing ratio), yet we may appropriately distinguish each as 

 the epoch of one of those important changes which tend towards the com- 

 pletion of the fabric ; namely, Childhood as ranging through the greater 

 part of the period of the second Dentition, Youth as characterized by that 

 increased evolution of the sexual organs, and by those general constitutional 

 changes accompanying that evolution, which altogether constitute Puberty, 

 and Adolescence as distinguished by that entire consolidation of the Osseous 

 skeleton, which is not completed until the full stature has been attained. It 

 will be convenient first to consider what is common to all these periods ; and 

 then to notice the features by which they are severally characterized. 



8G8. The passage from Infancy to Childhood may be regarded as marked 

 by the eruption of the " deciduous " Teeth ; by the termination of that direct 

 supply of food to the offspring, which is afforded until then by the mammary 



