Whether changes really occur in this region which are related to the sex is doubtful, and that bone growth is involved is very improbable.
(d) Abnormalities and Morbidities connected with Bone Growth, and its Hygiene. — The increased volume of blood and physiological work which centers about the various bony epiphyses at this period of augmented growth, where ossifica- tion is taking place so rapidly at so many points and gradually fusing bones into solid individuality, is also increasing the * The Child and Childhood in Folk-Thought. Alex. Chamberlain, p. 95.
8o THE PSYCHOLOGY OF ADOLESCENCE proportion of solid matter in those parts of bones previously ossified. Bibra's opinion that the proportion of carbonate of lime in the bones increases toward nineteen, to diminish later, while that of phosphate of lime conversely decreases at that age and increases later, lacks confirmation. Although the bones, because they are the hardest parts of the body and the last to decay, are our chief data for interpreting the past of paleontology, they are nevertheless the framework of the body only in a mechanical and not in a morphological sense; their development is not only later than that of the soft parts, but is dominated by them. Bones, like all other tissues, are composed of cells, penetrated by nerves and blood-vessels, are very plastic both to the normal forces of growth and to external influences, and are subject to many diseases. Ossification may be premature or excessive, and the bones become too large, dense, or heavy. The processes of mineralization may even encroach on cartilages, arteries, heart, muscles, etc., until they decay from overcalcification, or they may invade the joints until they become rigid. On the other hand, bone growth by which the skeleton is completed may be deferred and insufficient in its later stages, and its parts, its connections, or both, may be arrested, while in a group of diseases of defect, bone-cells may be broken up and bone even discharged by suppurative processes, and again, bones may grow perversely in form, proportion, or chemical composition. In rickets, the skeleton grows into many irreg- ular shapes, owing in part to abnormally compensated muscle tonus. Too much phosphate and carbonate of lime may make the bones so brittle as to cause spontaneous and recurrent frac- ture from the weight of the body. Defect of the mineral salts and excess of gluten and chondrin make them too soft and flexible. Finally, bones are not exempt from extremely well- marked types of invasion by micro-organisms.
If growth is excessive, there are often two kinds of so- called growing pains: First, that located in epiphyses or grow- ing centers of the bones, which are supplied with nerves and may become the seats of inflammation. These pains may seem seated in the bones, limbs, and perhaps most often near the neck of the femur and tibia, although almost no part of the body is entirely exempt from them. Adolescent tarsalgia and PARTS AND ORGANS DURING ADOLESCENCE 8l arthralgia have been described. The rapid bone growth fol- lowing fever may be attended with painful, though mild osteitis, periostitis, medullitis, and even hyperosteogenic ex- ostosis, especially in boys between eleven and twenty-two. Sec- ond, the bones may grow faster than the muscles or the skin; the latter then suffer from abnormal tension and are stretched and perhaps bloodless, especially on the thighs, because growth in the various tissues involved is not proportionate. This, too, is often acutely painful.
Very interesting is the intimate relation between sex organs and bones, as seen in cases of osteomalacia conse- quent upon ovarian or testicular defect or removal, and still more so in acromegalia. In this disease the bones of the face and limbs, after having reached their normal size, con- tinue to enlarge so as to greatly change the features and form. The hands and limbs are sometimes enormous. Changes in the thyroid gland, sex organs, and their functions and gen- eral nutrition are also common. Although these changes may be noticeable and become more rapid after thirty, they seem usually to originate at puberty, and by some, following Marie, are ascribed to disturbance in the pituitary body. It has been suggested that the normal growth of puberty is acromegalic, and that this process is a late recrudescence or continuation and excess of the rapid evolution of hands and feet, face, and limbs at the awkward age. I can find no more interesting case on record than one photographed and de- scribed at length by Marro,^ of a precocious boy who, besides the large bones characteristic of this disease, was at nine years and six months of age practically a mature man in beard, voice, intelligence, etc., and who four months after semicastration lost his beard and some other signs of abnor- mality.
Souza-Leite gives a brief history ^ of conceptions of acro- megalia since it was first recognized at the Salpetriere in 1886. It is, as the name indicates, a marked augmentation of the extremities, and often of the head. The rings, gloves, shoes, and hat are too small; the jaw, nose and cheeks enlarge; mus- • Revue scientifique, 1890, p. 801 et seq.
82 THE PSYCHOLOGY OF ADOLESCENCE cular force is at first increased and then decreased; the voice becomes deep, urination is profuse, and genital functions de- cline, and all these symptoms never occur in childhood, but always after puberty. After a long period of evolution it may remain stationary, but it rarely recedes. Patients generally grow feeble, rachitic, and perhaps die in syncope. Its chief activity is not only in the bones of the extremities, but at the extremity of the bones. The thymus, instead of disappear- ing as it should with youth, increases.
Excessive strain and tension at this period tend to vari- ous curvatures, lordosis, scoliosis, etc., so that too high pil- lows, sleeping in one position, ill-adjusted seats at school or on the bicycle, lacing, occupations that strain, confine, or require unnatural postures, are especially to be avoided at this age. It is necessary that the muscles should be used enough to keep them both flexible and growing with the bones, so that insufficient muscular development be avoided. They should not, however, be used enough to cause contrac- tures, for unequal or abnormal tension may warp the bones. Children should never be made to feel ashamed of their height, which they often form crouching habits to conceal, but should be proud of it, and stand and sit as erect as possible, and habitual cross-legged attitudes should be avoided. The thorax suffers from such easily avoidable causes perhaps even more than the pelvis, which may be contracted in the coccygeal aperture by sitting too low down on the back; while many young people who might go through life with strong chests and good busts fail to develop them and remain on a lower plane of vitality, unable to breathe deeply and well. Brain- work, if excessive or ill directed, may cause modifications of muscular tenacity that affect bone growth and bodily form and symmetry generally. Normal muscle tensions are thus of great importance during these plastic, and therefore vulner- able, years.
So plastic are they that Jager^ thinks the following illustrative of Meyer's law that pressures and tensions exert great influence on the development of the human skeleton. The length of each vertebra in child and man he found to * The Longitudinal Growth of the Human Bones, by Gustav Jager. In his Problems of Nature. New York, 1897, p. 154.
PARTS AND ORGANS DURING ADOLESCENCE S^ increase steadily downward from the second cervical to the fifth lumbar (except from the second to the sixth dorsal, which he ascribes to the arms). Reckoning the body weight as nearly two pounds per inch, each vertebra would have less weight to sustain than the one above and more than the one below it. This increase is therefore ascribed to the stimulus of increased pressure.
Bone growth needs lime, and our returns abound in ac- counts of eating chalk, pencils, plaster of Paris, and even mortar. These appetites are most often specified when growth is most rapid, as after a fever. Some think these freaks of appetites are less in hard-water regions, and that bone growth is retarded if only soft water is used. Some physicians hold very strong views upon this subject. Per- haps at this stage of growth children need lime somewhat as cattle need salt; that their milk, etc., should have slight lime admixtures, and that all foods and drinks of acidulous character need such compensation. Perhaps the nicotine and other alkaloid habits, to which this age is so prone, may also owe part of their strength to nutritive needs, which might be better interpreted and thus lose their morbid character.
Interesting in this connection is the wide-spread belief in the western parts of this country that hard water causes sterility. Especially in soda regions we are often told that chil- dren are few, and many cases are cited where children in such places are born only to households where the water is distilled.
B. Growth of Muscles. — The epithelial muscle plates are developed from the primitive segments of the central wall of the mesothelium. These cells elongate in the direction of the embryonic axis, and from them the circa two hundred and forty skeletal or voluntary muscles arise. These show their charac- teristic structure early in fetal life, and fibrillation appears soon after. The details of the development of the muscles is one of the most obscure chapters of embryology. It seems clear, how- ever, that both nerve and muscle fibers are well along in their development before they unite. In lower vertebrates the muscles are more or less segmented into myotomes by parti- tions and sclerotomes which cross them at each vertebra; but 84 THE PSYCHOLOGY OF ADOLESCENCE in man this is seen only in the deeper muscles nearest the spine. In general, the energy of the contraction of a muscle varies with the number, and its range with the lengths of its fibers. There is so wide a field of individual variation that Wiedersheim states that new muscles, not down in the text-books, can be found in nearly every human subject. He finds three classes of variations, viz., retrogressive and ves- tigial muscles, occasional or atavistic, and progressive or slowly developing muscles. Abnormalities are so frequent, and so completely connect man with normal apes, that he concludes that the chasm which separates them is entirely bridged so far as the muscular system is concerned, although this perhaps can not be so confidently stated of other systems. Variations are more frequent in the limbs than in the body, in the arms than in the legs, and in the hands than in the arms, suggesting here again that man breeds truer in the more fundamental than in the later acquired or accessory parts, which are less indispensable to life.
During pubescent growth the muscles increase in both length and thickness in both sexes, especially in boys, and their points of attachment to the bones become more pro- nounced. Oppenheimer thinks that at this period the mus- cular grows faster than any other tissue, unless it be fat in girls. Muscle growth is not only in the length and thick- ness of fiber, but it can no longer be doubted that new fibers are formed besides the primitive ones in animals and perhaps in man. In girls muscular growth is less pronounced, with the important exception of the uterine muscles, which acquire most of their development during these years.
In the human body of the adult male, considerably more than half the muscles, or 18,682 grams out of the total of 30,574 grams, are connected with the legs; 8,016 grams with the arms; and 1,708 grams with the back. The relation of the extensors of the forearm and head to that of the con- tractors is as 42 to 58.
We have no data to show just how much individual mus- cles grow with age. Several have attempted to determine the weight of the entire muscular system. Upon the six cases of Bischof and the much better work of Theile,* Miihlmann • Theile. Nova, acta der Kaiserl. Leip. Akad. des Naturforscher. Halle, 1884, PARTS AND ORGANS DURING ADOLESCENCE 8S concludes that at eight the muscles weigh 27.2 per cent of the entire body; at fifteen, 32.6 per cent; at sixteen, 44.2 per cent; at twenty-six, 45 per cent; and at none of the inter- mediate years he gives do they reach so high a proportion, but fall off slowly, and rapidly after forty-five, with the slight ex- ception of the age of forty-two, when they reach the doubtful ratio or 49 per cent.
Of all the special measurements of growing boys in this respect the best are still the girths of arms and legs made by Kotelmann, as follows, the figures being centimeters: Upper Arm Age.
Yr. abs. increase.
Bent.
Yr. increase.
Lower Leg Age.
Muscles of calf.
Yr. increase.
Bent.
Calf.
Yr. increase.
These measurements were made on the left upper arm at the upper third of the biceps region, and at the upper third of the calf when both limbs were straight and also at their maximal flexion. The relatively less increase of the leg as compared with the arm he thought not normal, and ascribed to sitting in school. In muscle girths at hips, thigh, calf, biceps, and forearm, Moon found that " the boy at fifteen is relatively to height superior to the boy at 86 THE PSYCHOLOGY OF ADOLESCENCE eleven, and more nearly the equal of the man." The growth of these girths follows closely that of bone girths, only the period of acceleration begins a year earlier in the muscles of the leg — that is, at twelve instead of thirteen. In these muscle girths the boy is relatively to height inferior to the man.
Age.
70 74 Girths.
Right thigh.
Left thigh.
Right calf.
Left calf.
Upper Upper Age.
Upper left arm.
Right forearm.
Left forearm.
Neck.
IIO no IIO III III III Breajjths.
Shoulder.
Nipples.
Waist.
Hips.
The best data for showing the growth in the size of the larger voluntary muscles are those by Dr. Hitchcock, who has measured Amherst students for many years and who gathers into the above table the average girths and breadths found among the students for each age. The numbers are mil- limeters: In the lower line above I have added from the same PARTS AND ORGANS DURING ADOLESCENCE 87 authority the gain, of each student, in each of the dimensions named, during his four years in college, most of them eighteen on entering, and twenty-two on leaving. Comparing these figures with those available from five other American col- leges, the difference in each respect is very slight, so that we have here the best account yet accessible of the growth of these muscles during the above years, a growth which is greatest in the upper arm, both flexed and relaxed. The neck, chest, and shoulder muscles seem here also to grow more than the waist and hip muscles, and those of the upper arm more than those of the thigh or calf. Although most of these meas- urements have been regularly taken on American college girls, I can learn of no treatment of the data to show growth.
Kotelmann's ^ measurement of boys in a Hamburg gym- nasium between the ages of nine and twenty-one showed many interesting results. He found that the difference of girth between the relaxed and contracted muscles of the upper arm at the point of greatest expansion of the biceps constantly in- creased with age; also that this absolute increase was ''dis- tinctly greatest at the age of puberty and decreased more and more backward to nine and forward to twenty-one." Both bent and contracted, the relative increase of girth became an- nually greater to the age of fifteen, and less and less to twenty-one. He also found that while the growth of the muscles of the lower thigh as measured by girth increased, it was steadily less relatively to that of the upper arm with increasing years, or the older the pupil the more the rate of increase in the muscles of the lower extremities fell behind those of the upper; this he ascribed to sitting. When the difference in girth of thigh contracted and relaxed was measured, this disadvantage of the leg to the arm was still greater. These muscles were growing less contractile just at the age when those of the upper arm were growing most. Yet in each respect puberty was the age of most rapid relative and absolute annual increment, this being greatest at fourteen and less both before and after.
From the estimates of Wertheim,^ it seems that the co- efficient of elasticity of the muscles diminishes in a marked ^ Die KSrperverhaltnisse der Gelehrtenschule. Berlin, 1879. ^ Annales de Chimie et de Physique, vol. xxi, 1847, p. 385.
88 THE PSYCHOLOGY OF ADOLESCENCE and rather steady way from infancy to old age, falling from 0.857 to 0.352; from twenty-one to thirty years in cohesion from 0.040 to 0.026 in kilograms pro i min.; and that for later years at least a marked decline in both these respects holds for the same qualities of nerves.
Sometimes the muscles grow in length more slowly than the bones, and then occur the " growing pains " so character- istic of this age, especially in boys, as we have seen. On the other hand, the muscles may grow more rapidly than the bones, and then the flexibility of joints often so extreme at this period of life is seen. The range of movements in joints is sometimes increased, though in some persons it is diminished. Sometimes muscular growth is not well distributed or is asymmetrical, and then new and perhaps abnormal positions of the body and limbs and new expressions of the face are seen. In morbid cases, arrest of growth of muscles may, like contractures, cause distortion of bones. Probably the most common disproportion in muscular development arises from the fact that the larger and more fundamental muscles, which move the greater joints, precede in their development the smaller, finer, or accessory muscles which move fingers, throat, lips, and make all the more delicate adjustments. This, along with the disproportion between bone and muscle growth, is one of the chief causes of the characteristic clumsi- ness of adolescent boys.
For the development of muscular function, see the next chapter, which is devoted to the subject.
C. Growth of the Heart and Blood-Vessels. — The heart, which seems to be phylogenetically a remnant of the prim- itive body cavity arising in vertebrates as a fissure in the meso- derm, according to Biitschli, begins its development in the em- bryo independently of the arteries and veins, and soon joins them, but not until after it has begun to beat. It is first a straight tube, and connects with the arterial system at its cephalic, and with the yolk or food supply at its caudal end. Gradually it becomes free, except so far as is needful for sup- port, and begins its evolution toward the adult form by blend- ing and twisting till all its chambers and valves are developed. The blood-vessels arise from a network in the area vasculosa, where groups of cells slowly aline themselves and become PARTS AND ORGANS DURING ADOLESCENCE 89 hollow. The first red blood-cells are probably proliferated and liberated cells from the endothelial lining of the vessels. These first elements of the blood slowly become flat, uniform, colored, and multiplied by division.
From their origin on to maturity the circulatory ele- ments are probably the most variable of all the great ana- tomical systems, not excepting even the muscles. Indeed, variations in the form, position, and arrangement of the blood-vessels are so great that in all but the most funda- mental respects it is often hard to tell what is normal and what is abnormal. Vascular variations constantly repeat not only fetal but prehuman animal arrangements. In general, the development is from fundamental to accessory, and arte- ries constantly compensate each other, not only in structure but in function, so that collateral circulation is easily devel- oped, if not especially provided for as in many plexi, the cir- cle of Willis, etc. Moreover, the heart continues to grow even to advanced age, although less rapidly after twenty- eight or thirty. Capillary changes are probably still more variable. Minot ^ goes so far as to say that " the immediate an- cestors of the vertebrates had no capillary vessels, but only a few large afferent and efferent trunks with a few anasto- moses," so that if variability and growth are inversely as either size or as ordinal development, a large field of un- known possibilities awaits exploration here. How much of this progressive capillary vascularity is pubertal we do not yet know.
This circulatory variability is nowhere so great as in those parts connected with the reproductive functions. We need but to instance the changes in the spermatic and ovarian blood-vessels as the testes and ovaries descend, the changes in the vaginal and uterine plexi, the pudic vessels, especially those going to and in the corpus spongiosum and the corpus cavernosum, the mammary, and most of all, the umbilical ves- sels, which are involved in both growth and function.
The mature heart ought to weigh about ten ounces in the male and eight in the female, or be from y-J-jj- to yit oi the weight of the body, and should be about the size of the tightly closed fist, increasing, according to Vierordt, to thirteen-fold 90 THE PSYCHOLOGY OF ADOLESCENCE its size at birth in males and twelve-fold in females. Before puberty the volume of the heart is nearly the same in both sexes, but between fifteen and twenty Benecke found its vol- ume to increase from an average of i6o to 225 cubic centi- meters; this increase being from 25 to 30 cubic centimeters greater for males, but continuing only about one cubic centi- meter per year for the next thirty years. This growth is not only in mass, but in the number of contractile fibers. Per- haps the best table here is that of Miihlmann, who, on the basis of Thoma's elaborate figures,^ brings together the results of four elaborate measurements.
Age.
Body weight.
Weight of heart.
Rel. weight of heart.
10 Gr.
Gr.
Per cent.
i I 12 iq 14 15 16 17 18 10 V 20 21 24 During the age of growth the increase of the heart keeps pace rather closely with that of the body, and this appears to be true for nearly all countries in Europe where these meas- urements have been made, and where the heart remains about 0.48 per cent of the body weight. This continued increase may be due to the fact that of all organs the circulatory are in the most favorable position to receive nourishment and oxygen from the blood. This increment may be so great as to seem almost pathological. After puberty hypertrophy of the heart is almost twice as frequent in males, and atrophy predominates in females. The heart now takes on the char- acter and does the work of an adult organ, and normally * Untersuchungen liber die Grosse und das Gewicht der an at. Bestandtheile des menschl, KOrpers. Leipzig, 1882.
PARTS AND ORGANS DURING ADOLESCENCE 9^ responds well to the increased activity imposed upon it by the expansion of the circulatory area. If there be temporary hypertrophy, which seems beyond normal limits in certain dimensions, this is soon compensated in normal individuals, and development becomes proportional.
The frequency of heart-beats is reduced at adolescence, but here again data differ widely. One writer computed a falling of from eight to eleven beats per minute between the ages of ten and fifteen. Guy's figures are as follows: Age.
Males.
Females.
79 76 73 92 82 80