68 



AGE. 



glands, are in a state of high development, 

 as indicated both by their ske and by their 

 tendency to disease. The stomach and duo- 

 denum are fully formed, but the sensibility 

 of their mucous membrane is adapted only to 

 the milk of the mother; any other kind of 

 food has a greater or less tendency to produce 

 irritation. This membrane is thick, extremely 

 villous and vascular, and consequently of a 

 rose-colour.* In young persons it assumes 

 a milky or satin-like appearance; in the adult 

 it becomes slightly ash-coloured, especially in 

 the duodenum and in the commencement of 

 the ileum ; in the old subject it is more de- 

 cidedly ashy. Its whitish appearance, according 

 to Andral,f is found either in very old persons 

 or in younger subjects who have died of ma- 

 rasmus. In the adult the small intestines, 

 according to Orfila,} bear a proportion of eight 

 to one as compared with the distance from the 

 mouth to the anus ; in the infant the propor- 

 tion is no less than twelve to one. The large 

 intestines are longer with respect to the small 

 intestines in the infant than in the adult; but their 

 calibre is proportionally smaller. Ascending to 

 the mouth we might be tempted to say that 

 there is evidence of incompleteness in the ab- 

 sence of teeth; but a moment's consideration 

 assures us that the organs collected in this part 

 are all eminently adapted to their function. 

 The food is already prepared by the mother, 

 and only needs to be extracted and conveyed 

 into the pharynx ; actions which are perfectly 

 achieved by the lips, cheeks, and tongue. 

 When the period has arrived at which this 

 food can no longer be furnished with safety 

 to the mother, and when all the purposes are 

 accomplished which were intended in this 

 close connexion between the two beings 

 purposes in all probability of a moral as well 

 as a physical character the infant is prepared 

 for a more independent existence by the emer- 

 gence of teeth. This event generally begins 

 about the sixth or seventh month by the appear- 

 ance of the two middle incisors in the lower 

 jaw ; these are followed by the corresponding 

 teeth in the upper jaw ; next are seen the 

 lateral incisors below and above : the rest 

 appear in the following order; the first molars, 

 the canines, and the second molars ; those of 

 the lower jaw having generally the priority 

 of emergence. The milk-teeth, as they are 

 called, by the end of the seventh year have 

 given way to the second and permanent series. 

 For the different characters of the two sets, 

 the order of their appearance, and other par- 

 ticulars, we beg to refer the reader to the 

 article TEETH. That the first series should 

 be only temporary is a necessary provision, 

 in conformity with the change in the conforma- 

 tion of the maxillary bones which ensues at 

 the same time. 



We must not leave the alimentary tract with- 



f Billard, Traitc des Maladies des Eafans, &c. 



t Precis d'Anat. Pathol. 



$ Le<jons de Mod. Leg. t. i. p. 62. 



This statement is at variance with that of 

 Mtckelj, who says that the small intestine is much 

 shorter in the early periods. Op. cit. t. iii. p. 424. 



out observing that the fibres of the stomach 

 and intestines in infancy and childhood are, 

 like those of the heart and other involuntary 

 muscles, more irritable than in afterlife ; hence 

 the contents of these viscera are propelled more 

 rapidly, and the evacuations are more frequent; 

 their tissue is also softer, and their colour more 

 approaching to white. 



The liver undergoes a great change after 

 birth both in form and in function. The pecu- 

 liar circulation of which it formed so important 

 an organ during fcetal life being abolished, 

 the left lobe which nearly equalled the right 

 in volume, is diminished to a third of its original 

 size. But while the umbilical vein and the 

 canalis venosus are obliterated, the vena portae 

 is developed, and the bilious secretion becomes 

 the predominant function. Of the further 

 changes which this organ experiences, we have 

 very little knowledge, except that the whole 

 bulk is greatly lessened, and that the colour of 

 its parenchyma becomes darker, and that it is 

 more subject to disease in after periods. Oc- 

 casionally we meet with instances in which the 

 foetal proportions of the liver continue through 

 life (Andral). The bile has not been carefully 

 examined with reference to particular ages, 

 but it is known to be less viscid and to contain 

 a smaller quantity of its peculiar principles 

 in infancy ; while its greater liability to con- 

 cretions at more advanced periods indicates an 

 alteration in its composition. The gall-blad- 

 der, though small at birth, contains bile, green 

 in colour and bitter in taste, and soon becomes 

 enlarged. 



The spleen also increases in volume, but 

 what alteration takes place in the progress 

 to maturity, in its function, must, of course, be 

 doubtful until the function itself be better 

 understood. Probably its enlargement is con- 

 nected with the distended condition of the 

 venous system. Of the changes in the pan- 

 creas and salivary glands, we know little more 

 than that their texture increases in firmness. 

 The lacteals, lymphatics, and their respective 

 ganglions have a very marked development. 

 It is to be regretted that no observations have 

 as yet been made upon the composition of the 

 chyle at different ages. There are doubtless 

 many alterations corresponding to the varying 

 activity of the digestive function, and to the 

 kinds of aliment used at those periods. 



So much for the organs and functions which 

 are concerned in augmenting or modifying the 

 nutrient matter. Before proceeding to those 

 of the relative life, we must allude to the 

 organs of excretion. The kidneys at birth 

 have not lost the traces of their lobular forma- 

 tion, but these are soon effaced. The weight 

 of these organs at birth is to that of the whole 

 body as 1-80; in the adult 1-240. The me- 

 dullary portion is more abundant than the corti- 

 cal in early life. The supra-renal capsules soon be- 

 gin to shrink from their fcetal size. The ureters 

 are large, and the bladder has a more elongated 

 form than in after periods ; it also occupies a 

 higher situation above the pelvis. The func- 

 tional qualities of these forms are not so well 

 ascertained as the analogy of their organization to 



