Human physiology (Volume 2) . e to be morbidlyaffected ; hence, the frequency of eruptive diseases, and of diar-rhoea, aphthae, croup, bronchitis, &c, many of which are of veryfatal tendency. Owing, also, to the susceptibility of the nervoussystem, convulsions, hydrocephalus, and other head affectionsare by no means infrequent. 2. CHILDHOOD. • Childhood may be considered to extend from the seventh to thefifteenth year, or to the period of puberty ; and it is particularlymarked by the shedding of the first set of teeth, and the appear-ance of the second. It is manifest, that in the growth of th
Human physiology (Volume 2) . e to be morbidlyaffected ; hence, the frequency of eruptive diseases, and of diar-rhoea, aphthae, croup, bronchitis, &c, many of which are of veryfatal tendency. Owing, also, to the susceptibility of the nervoussystem, convulsions, hydrocephalus, and other head affectionsare by no means infrequent. 2. CHILDHOOD. • Childhood may be considered to extend from the seventh to thefifteenth year, or to the period of puberty ; and it is particularlymarked by the shedding of the first set of teeth, and the appear-ance of the second. It is manifest, that in the growth of the jawswith the rest of the body, the teeth, which, for a time, may havebeen sufficient in magnitude and number, must soon cease to be » Delineations of the Origin and Progress of various changes of Structure whichoccur in Man, and some of the inferior Animals, Lond. 1828. b See the authors Elements of Hygiene, p. 138, Philad. 1835 ; and art. Longevityin American Quarterly Review, viii. 380, Philad. 1830. CHILDHOOD. 521. so ; hence, the necessity of a fresh set, which may remain per-manently. The process for the formation of the permanent teeth issimilar to that of the milk or temporary teeth; yet it presentssome remarkable points of difference ; and it affords us anothersurprising instance of the wonderful adaptation of means to defi-nite objects, of which we have so many in the human body. This process is well described by Mr. Bell,a whose opportuni-ties for observation have been unusually numerous, and whose zealand ability in his profession, as well as in the prosecution of natu-ral science, are well known. The rudiments of the permanent teeth are not original, and inde-pendent, like those of the temporary. They are derived from thelatter, and continue, for a considerable time, attached to, and inti-mately connected with them. At an early period in the forma-tion of the temporary teeth, theinvesting sac gives off a small pro-cess or bud, containing a portion ofthe essenti
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