Soon after graduating from a college where the chief studies of the senior year were under a president who summed up the great questions of the universe in a finishing way that gave a sense of finality unfavorable to further progress, I went to Leipzig to work under the leading physiologist of Germany, full of the conviction that the study of the mind could best be approached through that of the body. After hearing my case. Professor Ludwig suggested that I begin by studying certain functions of one of nearly a score of the muscles — the gastrocnemius — of a frog's leg. The mild dis- sipation of a somewhat too prolonged general culture and a little taste for easy, breezy philosophical speculation caused at first a strong sense of repugnance from so small and mean 130 THE PSYCHOLOGY OF ADOLESCENCE a theme. When it was well under way, however, and with the daily and personal guidance of this master in devising methods of experiment, planning new instruments for record and stimulus, suggesting fertile possibilities, showing the de- tails of all the technique, suggesting and placing in my hands new reading, etc., I found that I must know in a more accu- rate way than before certain definite points in electricity, which was the agent of stimulation; in mechanics, for the apparatus was complex, and there were possibilities of improvement and invention that might open up a new field of myological investigation; in the anatomy and physiology of other tissues for comparison; in chemistry in order to judge something of the effects of the artificial blood for constancy; and in mathematics in order to compute and analyze the con- traction curve into its components and to construct and inter- pret the records and tables. As the year progressed the history of previous views were studied and broader biological relations were seen. When summer came I packed a large case of books and read with might and main at a little summer resort on the Baltic, and began a second year of research upon this muscle with the most eager curiosity and zest. I reahzed that the structure and laws of action of muscles were the same in frogs as in men, that such contractile tissue was the only organ of the will and had done all man's work in the world, made civilization, character, history, states, books, and words. As the work went on, I felt that the mysteries not only of motor education and morality, but of energy and the universe, centered in this theme, from the persistent study of which, although in the end I made but an infinitesimal contribution to the vast body of certain scientific knowledge in the world, I learned several great lessons, viz.: that any object, however unattractive, may be a key to the greatest themes; that narrow specialization is now hardly possible, since evolution and the doctrine of the conservation of energy and comparative methods of study in every field have given us again a true universe instead of a multi verse; I understood the meaning of a really literal education and of a special as dis- tinct from a professional higher education, in a modern as opposed to a medieval sense, and I felt the omne tiitit puncttiiit oi nature's organic unity as a profound conviction that the GROWTH OF MOTOR POWER AND FUNCTION 131 world is lawful to the core. In fine, in the presence of this tiny object I had gradually passed from the attitude of Peter Bell, of whom the poet says " a primrose by a river's brim a yellow primrose was to him, and it was nothing more," up to the standpoint of the seer who plucked a " fiower from the crannied wall," and realized that could he but know what it was '' root and all and all in all," he would know what God and man is.
The muscles are by weight about forty-three per cent of the average adult male human body. They expend a large fraction of all the kinetic energy of the adult body, which a recent esti- mate places as high as one-fifth. The cortical centers for the voluntary muscles extend over most of the lateral psychic zones of the brain, so that their culture is brain building. In a sense they are organs of digestion, for which function they play a very important role. Muscles are in a most intimate and peculiar sense the organs of the will. They have built all the roads, cities, and machines in the world, written all the books, spoken all the words, and, in fact, done everything that man has accomplished with matter. If they are undeveloped or grow relaxed and flabby, the dreadful chasm between good intentions and their execution is liable to appear and widen. Character might be in a sense defined as a plexus of motor habits. To call conduct three- fourths of life, with Matthew Arnold; to describe man as one-third intellect and two-thirds will, with Schopenhauer; to urge that man is what he does or that he is the sum of his movements, with F. W. Robertson; that character is simply muscle habits, with Maudsley; that the age of art is now slowly superseding the age of science, and that the artist will drive out with the professor, with the anony- mous author of " Rembrandt als Erzieher "; that history is consciously willed movements, with Bluntschli; or that we could form no conception of force or energy in the world but for our own muscular effort; to hold that most thought involves change of muscle tension as more or less integral to it — all this shows how we have modified the antique Cice- ronian conception vivere est cogitari, to vivere est velle, and gives us a new sense of the importance of muscular develop- ment and regimen.^ * See my Moral Ed. and Will-Training. Ped. Sem., ii., pp., 72-89.
132 THE PSYCHOLOGY OF ADOLESCENCE Modern psychology thus sees in muscles organs of expres- sion for all efferent processes. Beyond all their demonstrable functions, every change of attention and of psychic states generally plays upon them unconsciously, modifying their tension in subtle ways so that they may be called organs of thought and feeling as well as of will, in which some now see the true Kantian thing-in-itself the real substance of the world, in the anthropomorphism of force. Habits even determine the deeper strata of belief, thought is repressed action, and deeds, not words, are the language of complete men. The motor areas are closely related and largely identical with the psychic, and muscle culture develops brain-centers as nothing else yet demonstrably does. Muscles are the vehicles of ha- bituation, imitation, obedience, character, and even of manners and customs. For the young, motor education is cardinal, and is now coming to due recognition, and for all, education is incomplete without a motor side. Skill, endurance, and perseverance may almost be called muscular virtues, and fatigue, velleity, caprice, ennui, restlessness, lack of control and poise, muscular faults.
For men, as we saw in the last chapter, and for animals, the age of sexual maturity is marked by an outburst of mus- cular growth, and also by great changes in its direction and distribution. It is the age when males engage in conflicts for females and develop organs of combat and also of pre- hension. There is a very close and but little understood relation between sexual and motor vigor, and many new notions and kinds of activity arise. The definite determina- tion of these changes is a new and very promising field of scientific activity. We first summarize the more important measurements of the motor changes typical of this age. Im- portant as these are, they all leave much to be desired.
Most of the common strength tests made in gymnasia are hardly more available as data for scientific measurement than are athletic records, and yet from both, interesting and valuable facts can be gathered, and there have been a num- ber of special studies of much worth.
Beginning with the lift, where the part played by back, legs, hips, and arms is not distinguished, Quetelet's table, where both hands were used, is as follows: GROWTH OF MOTOR POWER AND FUNCTION I33 Age.
Men.
From this table it appears that the Hfting power of girls from the ages of ten to twenty-seven, while constantly increas- ing, absolutely declines relatively to that of boys from 1,4 to 1.9; that this difference increases fastest from fifteen to eight- een, viz., from 29 to 51 kilograms. Both boys and girls gain most rapidly at sixteen and seventeen, but the gain of boys is more grouped about pubescent years, so that their increment curve is then greater, and also they continue to gain longer than girls.
Marro found the power to pull up on the Regnier dyna- mometer according to the following table of kilograms: Age.
Boys.
Girls.
II-I2 From this table it appears that from the sixteenth to the eighteenth years there is a sudden gain in boys and a less marked access of strength in girls in their sixteenth and nine- teenth years.
Hitchcock measured 742 Amherst students on entering THE PSYCHOLOGY OF ADOLESCENCE college and the same men three and a half years later with the following results: Age.
Number measured.
Actual number of units.
Per cent of gain.
l6 30 73 49 27 12 13 7 17 i8 IQ 20 21 22 24 Average From this table it appears that boys who enter college at six- teen and seventeen gain most during the course, but that all gain much. These results must be connected with the fact that most of them practised gymnastics during their course.
Hitchcock's averages for 4,000 Amherst students' back lift showed greatest gain at seventeen and eighteen, with no gain but slight loss from sixteen to seventeen, and reduced gain at twenty-one, a sharp rise at twenty-two, and no increase from twenty-three to twenty-six. From seventeen to twenty-three the average gain runs from 128 to 156.2 kilograms. Moon found the greatest increase of strength of back from fifteen to sixteen (91 to 102 kilograms, when his table ends), and next most from fourteen to fifteen (82 to 91 kilograms). With Erismann,^ the lifting power of arms and back, beginning with 82 at fourteen, reached 136 at nine- teen, and then increased more slowly to a maximum of 151 at thirty-three, some eight or nine years later than the max- imal clinching power. The greatest rate of gain was in the seventeenth and eighteenth years, and he thought strength generally increases fastest between fifteen and nineteen, but continues to gain at a diminishing rate to a maximum at from twenty-four to thirty-five, and then declines. Venn thought his pull, which was in large part a back movement, reached the maximum at twenty-three. Several observers * Ueber die KOrperliche Ent^rickelung der Fabrikarbeiter in Zentralrussland. Tubingen, 1889.
GROWTH OF MOTOR POWER AND FUNCTION 135 have expressed the opinion that for a time muscles of hips and back are not exceeded in growth rate by any others, whether measured by girth or strength.
The strength of the upper arms in the biceps region is remarkably augmented. According to Moon, at sixteen it is nearly fivefold what it is at eleven, and nearly doubles from fifteen to sixteen, increasing but very little from thirteen to fourteen. Hastings's measurements of 5,476 children are as follows: Age.
Kilos.
Strength of forearm, 1.
Kilos.
According to the Amherst tables, while strength in this part does not gain very rapidly after sixteen, it gains rather steadily to twenty-two. From sixteen to seventeen the forearm at Am- herst is gaining on the upper arm, and reaches the highest point at twenty-three, suggesting that its period of strength incre- ment may be a little later than the biceps, especially if we compare it with Moon's tables. The power to pull the body up at Amherst increased fastest from seventeen to eighteen, with years of low gain and often loss intervening, and reach- ing its maximum at twenty-three, as did dip. The latter increased by far the most rapidly from eighteen to nineteen, when pull not only did not increase, but fell ofif. It gained from twenty-one to twenty-two. There was also a year of loss in power to pull up.
Basing on the weight and the distance and height to which it was thrown, Vierordt computed the expenditure in " putting " for different ages, and found a great increase from the ages of ten to eighteen. This was both percentile and absolute for each two-year period. Roberts, Porter, and Gil- 136 THE PSYCHOLOGY OF ADOLESCENCE bert have tested wrist and arm lifts from six and a half to nineteen years. From these researches the very significant result is reached that boys acquire about one-half of their sixteen-year-old strength after eleven.
Gilbert tested about fifty boys and fifty girls from six to nineteen in lifting from the wrist, and found that from six to ten this ability nearly doubled in both sexes. From ten to nineteen it increased nearly threefold in boys and nearly twofold in girls. From fourteen to seventeen it nearly doubled in boys. The lifting power of the arm was, of course, far greater ( 171.9 kilograms: 27 kilograms boys at nineteen), but here also boys exceeded girls at all ages, and at nineteen, as with the wrist, they lifted nearly twice the weight girls could. The mean variations increased most during the period of most rapid growth.
With the dynamometer, Kotelmann ^ found that the power of the hands to press together against each other was nearly twice that of the arms to pull apart in a horizontal direction; that the former increased relatively to the latter to fourteen, and from that age to twenty-one suffered rela- tive but irregular decline. In both respects, " puberty is a marked turning-point." The pulling power of the arms rose steadily to fourteen, and then showed a great and sudden augment, and thereafter increased at a constantly slower rate to twenty-one. The same was true of this increment rela- tively. The muscles of the upper arm gain in strength more each year than does their girth, so that if the girth did not gain, this increase in power would be more each year up to twenty-one. At first the power of the arms to press together is nearly twice this power to pull, but the latter increases faster, so that at twenty-one the two are nearly equal. The clinching power of the hands is at all ages greater than the pressing power of the arms, and from ten to twenty-one the former gains upon the latter till at twenty-one it is one and three-fifths times greater.
Passing to the lifting strength of legs, Moon found that from eleven to sixteen boys increased from 125 to 213 kilo- grams, the greatest gain being at the thirteenth, fifteenth, and fourteenth vears of 2Q, 24, and 23 kilograms respectively, ^ Die KOrperverhaltnisse der Gelehrtenschule. Berlin, 1879.
GROWTH OF MOTOR POWER AND FUNCTION 137 as against ii kilograms in the twelfth year. The Amherst tables show greatest average gain at eighteen, with another distinct increment at twenty-one and twenty-two, with de- cline after twenty-three. Vierordt, basing on Quetelet's tables of weight and the highest average leap for boys each age from ten to eighteen, calculated the amount qf impulse or leg force for each two-year period. Beginning at ten to twelve with 25.61 kilometers, at twelve to fourteen it was 36.92; at fourteen to sixteen, 52.41; at sixteen to eighteen it was 72.67, showing marked absolute and some percentile gain. Moon found a marked increase between twelve and thir- teen corresponding with the growth of muscle girth, but so much greater than the latter as to suggest that the nerve- centers controlling these muscles were developing faster than the muscles themselves. The increase in the strength of the legs is so rapid for Moon's boys that at fourteen and fif- teen it surpasses that of men. The will is perhaps unable to excite the maximal contractive power of the muscles. Rivalry was found a potent stimulus in making these tests.
By placing a dynamometer between the knees, Kotel- mann* measured the power to press them together. He found that the pressure power of the thighs shows a pubertal increment that becomes annually greater till the age of fif- teen, and is then less, this increment being both relative and absolute. This increase is greater each succeeding year compared to the circumference of the thighs. The right adductors are slightly stronger than the left. In general, he found that the older the pupil the more the muscular develop- ment of the lower lagged behind that of the upper extremi- ties. Sedentary life also gave the muscles of the leg less contractibility than that of the arnr^. The strength of the latter increased relatively to arm girth, while that of the legs declined. Both leg girth and power showed distinct puber- al acceleration.
Vierordt doubts Kotelmann's conclusion that strength increases for a time faster than cross-section, falling back on the old law of their proportionality by Weber and even Bo- * Die KOrperverhaltnisse der GelehrtenschUler des Johanneums in Hamburg, von Dr. Med. u. Philos. L. Kotelmann. Zeitschrift des koniglich. preus. statis- tis. Bureau, 1879.
138 THE PSYCHOLOGY OF ADOLESCENCE relli. He fails to recognize that a law true of the excerpted muscle under artificial stimulus can not be applied to mus- cles in normal connection with the nervous system, and that the independent increase in the disposable energy of the latter might account for Kotelmann's increase if it be real. Dr. Gulick, a leading authority on physical training, informs me that near the dawn of puberty there is a distinct decline in the power to cHmb and' hang and otherwise move the body by the use of the hands. This comports well with the slow development of strength at the dawn of puberty just before the often sudden increment. This latter Bierent thinks directly due to the development and retention of seminal fluid. Amherst statistics show that tall students are best in the use of back, legs, and forearm, and short ones in lung power, dip, and pull up.
As far as any inferences can be based on these not entirely harmonious data, it appears that lifting power increases on the average fastest at sixteen, but hardly less rapidly at fif- teen and seventeen, and reaches a maximum at twenty-three or twenty-four, with a decline in the rate of augmentation in the later teens. Biceps power also increases, fastest at fifteen or sixteen, and power to pull the weight of the body up increases fastest a little later, from seventeen to eighteen, power in forearm having its fastest increment later than biceps, and dip later than pull, as power of the arms to pull apart comes later than the power to press together. Wrist power augments very fast, about doubling from six to ten, and nearly doubles again from fourteen to seventeen, pull up, dip, and forearm reaching a maximum at about twenty- three, or soon after. If Moon can be relied on, there is an almost explosive growth of leg power from thirteen to fif- teen, and the Amherst records suggest another marked aug- mentation at eighteen. All these directions of growth, per- haps especially that of leg power, seem not constant, but in periods of augmentation and diminution. Leg power seems to come first, then biceps and back, with forearm and power to repel later, and twenty-three is suggested as a culminating age. These inferences, however, are insecure. How this almost fulminating growth of leg and biceps power is related to phyletic flight, pursuit, modes of conflict, or sexual selec- GROWTH OF MOTOR POWER AND FUNCTION 139 tion, is a suggestive but tantalizing and at present unsolv- able problem. The rapid growth of locomotive organs sug- gests early migrations, and its selective advantages are conceivably manifold, and leg power is, as we shall see, very closely connected with sex. If sedentary life tends now to arrest its normal later development, its nascent period should be more utilized. That the power of pulling up the body and of otherwise moving it by the arms lags behind the growth of weight suggests that at this age, at least, the phyletic influ- ence of anthropoid arboreal life has ceased, or perhaps has been surpassed by more rapid growth of weight, while the sudden biceps increment suggests manifold possible inferences to prehistoric acts and occupations at this stage of development. That such inferences are now little more than conjectural is freely admitted. At best they are only suggestive. But if facts in both the history of the development of the race and in that of the individual have their chief value as those of one series shed light on those of the others, suggestiveness even has an illustrative value, because present studies in psycho- genesis indicate not only that this interval will be bridged, but that the arches that span it will some time bear a heavy traffic of scientific work and thought when they become the foundation of educational philosophy and practise.
The power of the hand to grip or squeeze is an interest- ing and significant measurement. The infant, like the ape, grasps with the fingers acting together, pressing inward upon the palm. The young child seizes a water glass, e. g., by inserting all the fingers in the glass and squeezing it against the palm, the root of the thumb remaining outside and use- less, and in climbing anthropoids use the hand as a hook. Slowly and relatively late in the child and the race is the thumb opposed. The dynamometer measures, although in part only, its power of acting against the fingers. This power, although well developed before, undergoes its most rapid acceleration in the teens. This, all tests show, although they differ from each other in many details. In Quetelet's table the greatest annual increase for boys' right hand is from fourteen to fifteen, and the next greatest increase is the year be- fore and the year after, but with a continued but diminishing THE PSYCHOLOGY OF ADOLESCENCE rate of increase to thirty. Kotelmann's table ends at fourteen, but the greatest increase is the last year shown. Pagliani ^ found the greatest increase from thirteen to fourteen years, but with marked annual increment to nineteen, when his table ends. Porter found the maximal increase from fourteen to sixteen. Chicago boys increased most rapidly from fourteen to sixteen, but continued to increase to twenty-one. Grigo- rescu,^ in testing ten boys of each age, found that from ten to thirteen strength of grip increased only from 42 to 48 pounds, but that at fourteen it ran up to 59, and at fifteen to 72. Venn ^ found that the mean squeeze of the two hands increased from nineteen to twenty-four only from 82 to 87.3 pounds, and thought that the power to both squeeze and to pull reached its maximum at about twenty-three to twenty- four, and then slowly declined. Erismann,* in testing 4,642 factory workmen of different ages in central Russia, found grip to increase in form most rapidly at sixteen and seven- teen. After nineteen it increased more slowly to a maximum at twenty-four to twenty-five, and then slowly declined, so that at the age of fifty-eight it equaled the strength of eighteen.
Age.
Actual in kilos.
* Sopra Alcuni Fattori dello Sviluppo Umana. Turin, 1876, p. 54.
* Zeits. f. Schulgesundheitspflege, 1892, p. 127. See also Compte Rendu de la Soci6t6 de Biologie, July 4, 1891.
* Cambridge Anthropology. Journal of Anthropology Institute, November, * Untersuchungen ttber die Korperlehre Entwickelungen des Russischen GROWTH OF MOTOR POWER AND FUNCTION H^ Erismann sums up by saying that in general the most rapid development of physical power occurs between the ages of fifteen and nineteen. From nineteen on the increase is slower, and twenty-six seems to be a stationary period. The maximum of greatest possible development of energy occurs from twenty-four to thirty-five; the maximum of lift- ing power comes a little later than that of the power to squeeze with the hands and also lasts longer. After thirty- five there is a gradual decline, which should not be marked before fifty. Although there is a remarkable coincidence between growth in weight and the pressure power of the hands, this paralleHsm is somewhat disturbed after eighteen, pressure power growing fastest, while from fourteen to eight- een weight increases fastest. Lifting power is far greater, and is in general related to power to squeeze as 2 J to i.
In general, we can say that boys almost double their eleven-year-old strength of dynamometer grip by the time they are sixteen. This is nearly the case with girls. Neither will ever double again, but boys will more than treble their eleven-year-old strength and girls will not. Erismann found a remarkable parallelism between increment in squeezing strength and in weight, except between fourteen and eight- een, when the former fell behind. Porter also noted this coincidence. Kline ^ concluded that the available power of a sudden squeeze was in proportion to the habitual vigor and energy of mental power and activity. Fere ^ thought that the educated and intelligent classes excelled the lower classes in this respect, even though the latter be muscle workers. It is now pretty well established that civilized man has greater strength of hand as tested thus than savages, and that adult men excel women by about one-third. If we compare num- bers and methods there are indications that somewhat favor fifteen as the year of fastest growth, with fourteen and then sixteen as ages of next fastest increment. After this wave there is a period of less rapid augmentation, with probably another lesser wave of increased rate in the very early twen- ties. The first period of increment seems to come later in