03 



AGE. 



impracticable to attend to all the circumstances that accelerate its 

 development, it requires the longest period that has been assigned to 

 it. Having acquired its full grow';h, it finally produces its gigantic 

 flower-stem, after which it perishes. This stem is sometimes as much 

 as 40 feet high, and is surrounded with a multitude of branches 

 arranged in a pyramidal form, with perfect symmetry, and having on 

 their points clusters of greenish-yellow flowers, which continue to be 

 produced for two or three months in succession. The native country 

 of the American Aloe is the whole of America within the tropics, 

 from the plains nearly on a level with the sea, to stations upon the 

 mountains at an elevation of between 9000 and 10,000 feet. From 

 these regions it has been transferred to almost every other temperate 

 country ; and in Italy, Sicily, and Spain, it has already combined with 

 the date and the palmetto to give a tropical appearance to European 

 scenery. 



Independently of its beauty and curiosity, this plant is applicable 

 to many useful purposes. Its sap may be made to flow by incisions 

 in the stem, and furnishes a fermented liquor called by the Mexicans 

 Pulque ; from this an agreeable ardent spirit, called Vino Mercal is 

 distillei The fibres of its leaves form a coarse kind of thread, and 

 are brought to this country under the name of Pita Flax ; the dried 

 flowering stems are an almost impenetrable thatch ; an extract of the 

 leaves is made into balls, which will lather water like soap ; the fresh 

 leaves themselves cut into slices are occasionally given to cattle ; and, 

 finally, the centre of the flowering stem split longitudinally is by no 

 means a bad substitute for a European razor-strop, owing to minute 

 particles of silica forming one of its constituents. 



AGE. The term of human existence is divisible into distinct 

 periods, each of which is distinguished by characters peculiar to itself. 

 These characters, as far as they are external, are obvious to every one ; 

 luit these external characters depend on internal states which are not 

 obvious, and which have been discovered only by careful and perse- 

 vering research. And the curious and interesting facts which those 

 researches have disclosed, show that the different epochs into which 

 life is divided are not arbitrary distinctions, but arise naturally out of 

 constitutional differences in the system, dependent on different 

 physiological conditions. The natural epochs of human life are six, 

 namely, the period of infancy, childhood, boyhood or girlhood, adol- 

 '<, manhood or womanhood, and old age. The space of time 

 included in the first four of these periods is fixed. In all persons after 

 the lapse of a certain number of years, a definite change in the system 

 uniformly takes place, in consequence of which the peculiarities which 

 distinguish one period give place to those which characterise the 

 succeeding. Thus the period of infancy, commencing at birth, extends 

 to the end of the second year, the point of time at which the first 

 dentition is completed : the period of childhood, commencing at the 

 close of the second year, extends to the termination of the seventh or 

 eighth year, the point of time at which the second dentition is com- 

 pleted : the period of boyhood or girlhood extends from the seventh 

 or eighth year to the commencement of the age of puberty ; that is, 

 m general, in this country, in the female, from the twelfth to the 

 fourteenth year, and for the male, from the fourteenth to the sixteenth 

 year : the period of adolescence extends from the commencement of 

 the period of puberty to the twentieth year of the female, and the 

 twenty-fourth of the male : the period of womanhood extends from 

 the twentieth, and of manhood, from the twenty-fourth year, to an 

 age neither determined nor determiuable with any degree of exactness ; 

 because the point of time at which mature age lapses into old age 

 differs in every individual. It differs in many cases by a considerable 

 number of years ; and it differs according to primitive constitution, to 

 the management of early infancy and childhood ; according to regimen, 

 exercise, occupation physical and mental, and the several other 

 circumstances included under the general term ' mode of life.' 



It is, an observation familiar to every one, that some persons are 

 older at fifty than others are at seventy, while instances every now 

 and then occur in which an old man who reaches his hundredth year 

 retains as great a degree of juvenility as the majority of those who 

 attain to eighty. The period extending from the age of thirty or forty 

 to that of extreme old age is then the only variable period in the term 

 of human existence ; the only period not fixed by limits which it is 

 I the power of man materially to extend or abridge. 



The changes which take place in the system at the different epochs 

 of life consist of changes in the physical condition of the body, and 

 are intimately connected with and mainly dependent on the operation 

 of a principle of consolidation, the influence of which, commencing at 

 the first moment of existence, continues, without intermission, until 

 the last moment of life. By this principle the body is changed, first 

 from the state of a fluid into that of a solid ; and next, from a soft 

 and tender solid, into a solid which slowly, imperceptibly, but never- 

 theless uninterruptedly, increases in firmness and hardness. 



When first the human embryo becomes distinctly visible, it is 

 almost wholly fluid, consisting only of a soft gelatinous pulp. 

 [H'ETt's.] In this gelatinous pulp solid substances are formed, which 

 gradually increase, and are fashioned into organs. These organs, in 

 their rudimentary state, are soft and tender, but, in the progress of 

 their development, constantly acquiring a greater number of solid 

 particles, the cohesion of which progressively increases, the organs at 

 length become dense and firm. As the soft solids augment in bulk 



AGE. 94 



and density, bony particles are deposited, sparingly at first and in 

 detached masses, but accumulating by degrees : these, too, are at 

 length fashioned into distinct osseous structures, which, extending in 

 every direction, xmtil they touch at every point, ultimately form the 

 connected bony frame-work of the system. This bony fabric, like the 

 soft solid, tender and yielding at first, becomes by degrees firm and 

 resisting, fitted, as it is designed, to be the mechanical support of the 

 body, and the defence of all the vital organs. 



While the osseous system is thus extending in every direction, and 

 everywhere increasing in compactness, the progressive consolidation 

 of the body is equally manifest in all the tissues which are composed 

 of the cellular membrane as well as in all those which possess a fibrous 

 nature. The membranes, the ligaments, the tendons, the cartilages, 

 gradually increase in firmness and elasticity, and proportionally 

 diminish in flexibility and extensibility ; and this change takes place, 

 to a considerable extent, in the muscular fibre also, as is manifest from 

 the toughness of the flesh of animals that are used for food, the degree 

 of which every one knows is in proportion to the age of the animal ; 

 and from the conversion in extreme old age, in many parts of the 

 body, of muscle into tendon, a denser material being substituted for 

 the proper muscular fibre. 



The steady and increasing operation of the principle of consolidation 

 is still more strikingly manifest in the deposition, as age advances, of 

 bony matter in tissues and organs to which it does not naturally 

 belong, and the functions of which it imm^liately impairs and 

 ultimately destroys. The textures in which these osseous depositions 

 most commonly take place are membranes, tendons, cartilages, and 

 the coverings of the viscera, but above all the coats of the blood-vessels, 

 in consequence of which these highly flexible, elastic, and moveable 

 organs become firm, rigid, and immoveable. But even when not 

 converted into bone, several of these structures lose their flexibility 

 with advancing age, and acquire an increasing degree of rigidity. This 

 is strikingly manifest in all the parts of the apparatus of locomotion ; 

 in the joints, the mechanical contrivances for facilitating motion, and 

 in the muscular fibre, the generator of the power by which motion is 

 produced. The joints in old age are less pliable, less elastic, and more 

 rigid than in youth ; first, because the ligamentous and cartilaginous 

 structures of which they are composed are more dense and firm ; and, 

 secondly, because the oily matter which lubricates them, and which 

 renders their motions easy and springy, is secreted in less quantity, 

 and of inferior quality. Induration and proportionate deterioration 

 take place then in the muscular fibre, the origin of the motive power, 

 and in the joint, the instrument by which the operation of the motive 

 power is facilitated ; and consequently the movements become slower, 

 feebler, less steady, less certain, and less elastic. 



But among all the changes induced in the body by the progress of 

 age, none is more remarkable, or has a greater influence in diminishing 

 the energy of the actions of the economy, and in causing the ultimate 

 termination of all those actions in death, than the change that takes 

 place in the minute blood-vessels. The ultimate divisions, or the 

 smallest branches of the arteries and veins, the capillary vessels, as 

 they are termed, are exceedingly abundant in the early periods of life, 

 and are as active as they are numerous. The capillary arteries, the 

 masons and architects of the system, by the agency of which all the 

 structures are built up, and all the parts of the body grow and are 

 developed, are numerous and active in the early stages of life, while 

 they are carrying on and completing the organisation of the frame. 

 But from infancy to childhood, from childhood to youth, from youth 

 to maturity, and from maturity to old age, the number and activity of 

 these vessels progressively diminish. Their coats, like other soft 

 solids, increase in density and rigidity ; their diameter contracts, many 

 of them become completely impervious and ultimately disappear. 

 The diameter of the capillary veins, on the contrary, enlarges. The 

 coats of the veins, originally thinner than those of the arteries, instead 

 of thickening and contracting, seem rather to grow thinner and more 

 dilatable : hence their fulness, their prominence, their more tortuous 

 course, and their greater capacity. At the two extreme periods of 

 life the quantity of blood contained in these two sets of vessels is 

 completely inverted. In infancy, the proportion of blood contained 

 in the capillary arteries is greater than that contained in the capillary 

 veins ; in youth, this disproportion is diminished ; at the period of 

 maturity, the quantity in one set, nearly if not exactly balances that 

 in the other ; in advanced age, the preponderance is so great in the 

 veins, that these vessels contain probably two-thirds of the entire mass. 

 This difference in the distribution of the blood, at the different epochs 

 of life, affords an explanation of several important phenomena 

 connected with health and with disease. It shows, for example, why 

 the body grows with so much rapidity at the early periods of life ; 

 why it remains stationary at the period of maturity ; why it diminishes 

 in bulk as age advances ; why a plethoric state of the system affects 

 the arteries in youth, the veins in age ; why hfemorrhage, or a flow of 

 blood, is apt to proceed in the young from the arteries, and in the 

 aged from the veins ; and so on. 



The growth of the heart does not keep pace with the extension of 

 the sanguiferous system, nor does its force increase with the augmenting 

 density and resistance of the solids ; hence there is a disturbance of 

 the balance between the forces of propulsion and of extension which 

 increases with advancing age ; the diminished energy of the heart being 



