FORMATION OF THE TISSUES TEETH. 497 



Second Bicuspid 11 years 



Cuspidati 12 to 12 



Second Molars 12^ to 14 



The following are the results of the application of this test, in a large number of cases 

 examined by Mr. Saunders. Of 708 Children of nine years old, 530 would have been 

 pronounced by it to be near the completion of their ninth year; having the central, and 

 either three or four lateral, incisors fully developed. Out of the remaining 178, it would 

 have indicated that 126 were 8 years old, as they presented one or two of the Lateral 

 Incisors; and the 52 others would have been pronounced 8 years old, all having three or 

 four of the Central Incisors. So that the extreme deviation is only 12 monlhs; and this 

 in the inconsiderable proportion (when compared with the results obtained by other 

 means) of 52 in 708, or 7 per cent. Again, out of 338 children of 13 years of age, 294 

 might have been pronounced with confidence to be of that age, having the Cuspidati, 

 Bicuspid, and Second Molars, either entirely developed, or with only the deficiency of 

 one or two of either class. - Of the 44 others, 36 would have been considered as in their 

 13th year, having one of the Posterior Molars developed; and 8 as near the completion 

 of the 12th, having two of the Cuspidati, and one or two of the Second Bicuspid. In all 

 these instances, the error is on the favourable side, that is, on the side on which it is 

 calculated to prevent injury to the objects of the inquiry; in no instance did this test 

 cause a Child to be estimated as older or more fit for labour than it really was. 



m. The value of this test, as compared with that of Height, is manifested by a striking 

 example adduced by Mr. Saunders. The height of one lad, J. J., aged 8 years and 4 

 months, was 4 feet and of an inch ; that of another boy, aged 8 years and 7 months, was 

 only 3 feet 7| inches. According to the standard of height adopted by the Factory Com- 

 missioners (namely 3 feet 10 inches), the taller lad would have been judged fit for labour, 

 whilst the shorter would have been rejected. The Dentition of the latter, however, was 

 further advanced than that of the former: for he had two of the Lateral Incisors, whilst 

 the former had only the Central ; and the determination of their relative physical powers, 

 which would have been thus formed, would have been in complete accordance with the 

 truth. The Elder boy, though shorter than the other by 5 inches, possessed a much 

 greater degree both of corporeal and mental energy, and his pulse was strong and regu- 

 lar; whilst that of the younger lad, who was evidently growing too fast, was small and 

 frequent. An instance even more striking has come under the Author's own observation. 



636. The development of the Human Tooth can only be rightly understood, 

 when it is compared with the same process in the inferior animals. Thus in 

 certain Fishes, as the Shark, the tooth is completed, without the formation of 

 the matrix ever having proceeded beyond the first or papillary stage ; and re- 

 mains attached to the mucous membrane oniy of the mouth. In many other 

 Fishes and in Serpents, the follicular and saccular stages are completed ; but 

 the enamel-organ is not developed. It is evident, then, that the papillary pulp 

 alone is concerned in the formation of the real tooth substance. From the 

 description of Purkinje and Ra^chkow, it appears that the parenchyma of the 

 papilla is composed of minute spherical cells, the free surface of which is 

 covered by a peculiarly dense, structureless, pellucid membrane (basement 

 membrane ?) and it is within this that the formation of the Dentine commences. 

 Blood-vessels soon penetrate the granular pulp, form several anastomoses in 

 their course through its substance, and terminate in a rich and delicate network 

 of capillaries, on that part of the surface of the pulp where the Dentine has 

 begun to be formed. The cellules of the pulp immediately beneath the pre- 

 formative membrane, have a more elongated form than the rest, and are placed 

 either vertically or at an acute angle with the membrane. This appears to be 

 a stage of transition towards the structure, which is afterwards characteristic 

 of the Dentine ; but the actual nature of the transformation has not yet been 

 clearly demonstrated. As the outer layer of cells becomes calcified, those of 

 the layer beneath elongate themselves, and arrange themselves regularly in 

 preparation for the same change ; and so on, until the greater part of the pulp 

 is ossified. Hence, when young animals are fed on madder, their teeth are 

 marked by a number of concentric rings of colouring matter. As already men- 

 tioned ( 635, c), the Enamel is formed by the calcification of the prismatic cells, 



42* 



