AGE. 



we proceed to the organs of circulation, similar 

 conditions are observable. In the heart the seve- 

 ral cavities, valves, and fibrous arrangements are 

 duly proportionate to each other, and possess such 

 qualities of firmness, pliancy, extensibility and 

 contractility as are required for receiving, expel- 

 ling, agitating, and keeping in separate compart- 

 ments the two different kinds of blood ; the 

 arteries are found resistent enough to hold the 

 blood within their calibres, and at the same 

 time elastic enough to adapt themselves to the 

 varying quantity of their contents, while the 

 veins are found so organized both as to the 

 muscularity of their coats, and to the perfection 

 of their valves, as to be quite capable of con- 

 veying the fluid back to the heart. Not less 

 complete is the apparatus of respiration, 

 whether we regard the development of the 

 diaphragm, or the elasticity of the thorax, or 

 the cellular and tubular arrangements in the 

 lungs and their appendages. For affording the 

 necessary conditions for the occurrence of those 

 molecular motions which constitute deposition 

 and absorption, and upon which secretion also 

 depends, we find an infinite number of capillary 

 tubes well formed for supplying the fluids from 

 which new particles may be taken, and to which 

 old ones may return, and so disposed as not to 

 interfere with the action of any supposable 

 chemical affinities. If we next direct our at- 

 tention to the organs of the animal functions, 

 an opposite set of facts will directly meet us. 

 In the locomotive system, the bones are dis- 

 covered imperfectly ossified, the muscles de- 

 ficient in fibrin, and the tendons and ligaments 

 in firmness and density. Of the organs of 

 sensation it may be said, in general terms, that 

 the mechanism employed in the application 

 of the appropriate stimulus is, for the most part, 

 incomplete, while a difference is also observa- 

 ble in certain properties of the nervous sub- 

 stance. 



From this view it might at first be con- 

 cluded that, in order to trace the changes that 

 ensue between the commencement of extra- 

 uterine life and the attainment of maturity, we 

 have only to look for them in the organs of 

 the relative life. But the survey that we are 

 about to take of the changes in question will 

 show that the other class of organs are by no 

 means exempt from alteration, although the 

 changes are not those of development. They 

 will be found to have reference to degree or 

 amount of function rather than to capacity. 



The external characters of the infant just 

 eliminated from the uterus at the full period of 

 gestation are as follows: the integuments 

 are thin, tender, and covered with a white 

 unctuous matter ; the nails just reach the ends 

 of the fingers ; the trunk and limbs are round 

 and plump; and the articulations are in a 

 state of flexion. The average weight of the 

 body is about six or seven pounds ; the length 

 varies from seventeen to twenty-one inches, 

 sometimes falling short of or exceeding these 

 limits. The point which lies midway between 

 the two extremities is at the umbilicus. The 

 dimensions of the head and of the abdomen 

 are very large in proportion to the other cavities, 



and as compared with their own measurements in 

 after periods of life. The pelvis looks con- 

 tracted, the thorax flattened at its sides and 

 prominent in front, and the lower extremities 

 are less developed than the upper. A line 

 drawn from the occiput to the chin measures 

 five inches and three lines ; from the occiput 

 to the forehead four inches and three lines ; 

 and from the vertex to the base of the skull 

 three inches and six lines. The circumference 

 of the head, taken along the course of the 

 median line, is from thirteen to fourteen inches ; 

 but taken horizontally, and passing over the 

 parietal protuberances, it seldom measures 

 more than ten or eleven inches. The contrast 

 between this general aspect and that of a full- 

 grown man is too obvious to require any repre- 

 sentation of it here. 



The characters of the interior will be best 

 described and understood by examining ana- 

 lytically the several apparatuses of the func- 

 tions. Of the latter the most simple and 

 primitive is assimilation, consisting of certain 

 molecular motions which maintain, repair, and 

 mould the organic tissues. We have already 

 observed that the requisites for this function 

 are perfect in the new-born infant; a copious 

 supply of the fluid from which the textural 

 particles are to be elaborated, a ready ingress 

 for this fluid, and a no less ready egress for 

 that which receives the particles no longer 

 required in the process. All that we know 

 of the mechanism employed is a porous ex- 

 tensile substance, varying in its chemical con- 

 stitution according to the nature of the tissue. 

 Porosity is resolvable into a collection of 

 infinitely minute tubes, and the degree of 

 porosity is, therefore, determined by the 

 number of the tubes ; the extensibility depends 

 on the composition of the tubes. The tissues 

 of the infant are soft, they abound in fluids, 

 and are more capable of imbibition or artificial 

 injection than at later periods of life ; this 

 being consequently possesses a complete me- 

 chanism of nutrition. But this mechanism 

 can be of little utility unless the nutrient 

 fluid be supplied liberally, and after furnish- 

 ing the atoms for the formation of the several 

 textures give place to fresh supplies. These 

 conditions are afforded by the arteries and 

 veins. 



There is no period of human existence in 

 which the processes of interstitial growth are 

 so active as in infancy, whether they be 

 instanced in the accretion of matter, in the 

 change of composition, or in the modification 

 of form. This fact is in harmony with the 

 state of the capillary system just described, 

 and it will be found to correspond no less 

 with the relative construction of the arteries 

 and veins. The function of the former of 

 these is to convey the blood into the tissue, 

 of the latter to take it away ; consequently 

 in a part where the growth is most energetic, 

 we might, a priori, expect that the former 

 would be more numerous, capacious, and 

 distensible. This is well known to be the 

 case from actual observation, partly of the 

 effects of artificial injection, and partly of 



