496 OF NUTRITION. 



removed; when its crown falls off, leaving room for the permanent tooth to supply its 

 place (Fig. 130, p /). This absorption is usually regarded as due to the pressure of the 

 Permanent tooth, but this does not appear to be the case; for it is mentioned by Mr. Bell, 

 that it is not an uncommon occurrence for the root of the temporary tooth to be wholly 

 absorbed, and for the crown to fall out spontaneously, long before the succeeding tooth 

 has approached the vacant space. The same has been remarked by Mr. Bell, of the 

 cavity in the jaw which is formed for the reception of the sac of the Permanent tooth, at 

 the time that it buds off from that of the milk-tooth; the excavation being often seen to 

 commence before the new sac is formed. Hence, although the two processes, growth 

 and absorption, are usually cotemporaneous in each instance, they are by no means 

 dependent on each other. Still it would seem that the existence, if not the pressure, of 

 the new Tooth is necessary to determine the absorption of the old; for cases are not 

 unfrequent, in which the Temporary teeth retain their situation in the mouth, with con- 

 siderable firmness, until adult age, the corresponding Permanent ones not having been 

 formed. 



k. In the successive replacement of the Milk-teeth by the Permanent set, a very regular 

 order is usually followed. The Middle Incisors are first shed and renewed, and then the 

 Lateral Incisors. The Anterior Milk Molars next follow; and these are replaced by the 

 Anterior Bicuspid teeth. About a year afterwards, the Posterior Milk Molars are shed, 

 and replaced in like manner, by Bicuspid teeth. The Canines are the last of the Milk- 

 teeth to be exchanged; the development of the new ones not taking place until the 12th 

 year. In the succeeding year, the Second pair of True Molars appears; the third pair, 

 or denies sapientise,are seldom developed until three or four years subsequently, and often 

 much longer. It has been recently proposed* (and, from the evidence adduced in its 

 favour, the proposition would seem entitled to considerable attention) to adopt the suc- 

 cessive stages in the Second Dentition, as standards for estimating the physical capabili- 

 ties of Children, especially in regard to those two periods which the Factory Laws render 

 it of the greatest importance to determine, namely, the ages of nine and thirteen years. 

 Previously to the former, a Child is not permitted to work at all ; and up to the latter, it 

 may be only employed during 9 hours a day. The necessities or the cupidity of Parents 

 is continually inducing them to misrepresent the ages of their children; and it has been 

 found desirable, therefore, to seek for some test by which the capability of the Child may 

 be determined, without a knowledge of its age. A standard of Height has been adopted 

 by the Legislature for this purpose; but upon grounds which, Physiologically considered, 

 are very erroneous ; since, as is well known, the tallest children are frequently the weak- 

 liest. According to Mr. Saunders, the degree of advance of the Second Dentition may 

 be regarded as a much more correct standard of the degree of general development of the 

 organic frame, and of its physical powers; and it appears from his inquiries, that it may 

 be relied on as a guide to the real age, in a large proportion of cases; whilst no serious 

 or injurious mistake can ever arise from its use. It may happen that local or constitu- 

 tional causes may have slightly retarded the development of the Teeth; in which case 

 the age of the individual would rather be under-estimated, and no harm could ensue: on 

 the other hand, instances of premature development of the Teeth very rarely, if ever, 

 occur: so that there is no danger of imputing to a Child a capability for exertion which 

 he does not possess, as the test of height is continually doing. Moreover, if such an 

 advance in Dentition should occur, it might probably be regarded as indicative of a cor- 

 responding advance in the development of the whole organism; so that the real capa- 

 bility would be such as the teeth represent it. 



/. The following is Mr. Saunders's statement of the Ages, at which the permanent teeth 

 respectively appear. The first True Molars usually make their appearance towards the 

 end of the 7th year. Occasionally one of them protrudes from the gum at 6, or more fre- 

 quently at 6 years of age; but the evolution of the whole of them may be regarded as 

 an almost infallible sign of the Child's being 7 years old. In other instances, however, 

 where the tooth on one side of the mouth is freely developed, it is fair to reckon the two 

 as having emerged from their capsule; since the development of the other must be con- 

 sidered as retarded. This rule only holds good, however, in regard to teeth in the same 

 row; for the development of the teeth in either jaw must not be inferred from that of the 

 corresponding teeth in the other. With this understanding, the results of the application 

 of the following table will probably be very near the truth. 



Central Incisors developed at . . 8 years 



Lateral Incisors 9 



First Bicuspid 10 



* "The Teeth a Test of Age, considered with reference to the Factory Children." By 

 Edwin Saunders. 



