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formly well fed and clothed. Therefore, it is believed that they may be taken to represent normal Chicago children, living under good conditions. From these tests and measurements, tables of norms have been compiled. As we were obliged to compile the data several times, we have been able to watch the changes which added numbers have produced. These changes of the norms from the addition of the last set of cards representing the measurements of about 50 pupils of each year of age, between the ages of 6 and 16, have been so slight that it is believed that these norms are fairly representative of the class of pupils tested for these years. And probably large additions to these figures, if the data were taken from the same class of pupils, would but slightly change the averages thus established. The norms for the upper years, 16 to 21, and also for the kindergarten ages, 4 to 6, on account of the paucity of numbers can hardly be considered so completely established. In these compilations averages have been used rather than medians, although the difference between averages and medians proved insignificant. The mathematical computations were made by means of a comptograph; so "machine accuracy" in the results has been obtained. That these results may be quickly and clearly understood, charts have been made of the growth and development along the lines in which tests and measurements have been made. It is not assumed that a single child grows at exactly the same regular movement upward as is shown by the tables and charts, yet it is believed that ordinarily children do not differ widely from this rate, and the average of a small number of the same class of boys and girls taken from year to year would give us figures almost identical with the results of these compilations. So these tables fairly show laws of growth and physical development.

There is a prevalent belief, growing out of the evolutionary doctrine of the survival of the fittest, that the average represents the ideal type. As these measurements must include many imperfect specimens, children who through disease, malnutrition, and other insalutary conditions have failed to attain the growth and development that they otherwise would have reached, in all probability the evolutionary ideal type will be found somewhat above the average in each measurement. These averages are representative of the class of children measured, and are highly important as a basis of comparison. It may be added that comparison of these measurements with those taken in other cities shows the superiority of this class of Chicago school children in both size and physical development.

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Birthday norms.-In compiling these norms the age at the last birthday was used. It was assumed that the actual average age for any year would be that year and about six months. When the average ages were made out, it was found, as will appear on the table, that in some years the ages averaged above the half year and in some below. In order to ascertain the norms for the exact years and half years the daily and monthly increments were calculated. The increment between any two average ages divided by the exact number of days between those ages gives the average daily increment, and this multiplied by 30 gives the average monthly increment. On this basis a table of norms computed to integral years and half years for the ages from 6 to 18 has been calculated and is given, together with a table of the monthly increments. In these tables where the averages of the girls are greater than the averages of the boys for corresponding ages, the measurements have been printed in heavy-faced type.

These norms, computed to the integral years, are, for the sake of convenience, termed "birthday norms."

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TABLE III.-Average monthly increment of birthday norms.

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Height was measured by means of an adaptation of the Bertillon stadiometer.. The heels of the shoes were calipered, and the height of the shoe heels taken from the gross height gave the net height. This upon trial proved almost identical

with the height when taken without shoes. The results of the compilation of height standing and height sitting will be found in Table I. It will be noted that the average girl is shorter than the average boy when they enter the kindergarten, but just before reaching 11 years of age, owing to a slackening of the boy's rate of growth and an acceleration of the girl's, the average girl becomes taller than the average boy and remains taller till they reach the age of 15 years. At this period the girls seem to be exhausted in the race, and the boys surpass the girls in height and continue to increase the difference in stature for a number of years.

As in height standing so in height sitting. When the pupils enter the kindergarten the average boy is slightly taller when seated than the average girl, but just before attaining the age of 11 years the average girl surpasses the average boy in height sitting. This again seems due as much to a retardation in the boy's rate of growth as to an acceleration in the girl's rate of growth. The average girl continues taller when seated than the average boy till nearly 16 years, or almost a year longer than her height standing exceeds the height standing of the average boy. This shows that the more rapid growth of the boy at this age is chiefly in the lower extremities rather than in the trunk.

GROWTH IN WEIGHT.

As we found in stature so we find in weight that the average boy exceeds the average girl during the early years of school life. During the three years from 12 to 15 the average girl is heavier than the average boy. Soon after 15 is reached the boy surpasses the girl in weight and he continues to increase in weight more rapidly than she does for a number of years. It will be noted that the average girl surpasses the average boy in weight at about a year later than her stature exceeds his. The tables of weight and height show that the girls continue to increase in weight for a longer period than they increase in height.

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FIG. 2.

THE DEVELOPMENT OF STRENGTH.

Strength of grip was tested at first by an ordinary 2-spring dynamometer, but an attempt to test the young children with this instrument proved that it was entirely unsuited to the size of their hands. Those with the smallest hands were forced to use a different set of phalanges from those which the adult would use on the same instrument. Again, it was found that the adult could make his best record only when the instrument was suited to the size of this hand. For this reason we were forced to devise a new dynamometer which could be adjusted to the size of the hand. This new adjustable grip dynamometer is represented in fig. 2. It is set by changing the distance between the bars of the inner and outer stirrups. This is accomplished by whirling the inner stirrup, a screw thread passing through a nut below the dial, causing the protrusion or withdrawal of the stem of the stirrup. A distance between the bars corresponding to about one-half of the distance from the

place where the thumb joins the hand, to the end of the fingers, was found best suited to most hands.

Each pupil was given several trials of strength and the best result obtainable was recorded. It will be seen from Table I that the boys surpass the girls in strength at all ages; even in the kindergarten the average boy is stronger in his left hand than the average girl is in her right hand, and during the early years of adolescence this differentiation of the sexes becomes very striking. These facts were shown in Dr. Christopher's report and have been fully confirmed by the compilation from the larger numbers.

DEVELOPMENT OF VITAL CAPACITY.

The term vital capacity is used here to signify the amount of air that a person can expire after a forced inspiration.

Vital capacity was tested by means of a wet spirometer. In this test, as in the test of strength, the child was allowed repeated trials until he fell short of his previous efforts and the best mark attained was recorded. The boys show greater breathing capacity from the first, the difference becoming marked during adolescence. The great breathing capacities of the boys who were in training for football and the girls who played basket ball were in strong contrast with those who took little physical exercise, which suggests that vital capacity increases and decreases with the amount of one's activity, and so, in connection with size, is an index of the rate of metabolism.

THE DEVELOPMENT OF ENDURANCE.

A modification of Mosso's ergograph made possible the study of endurance and fatigue. This instrument gives a graphic record and a measure of the work done under certain fixed conditions by a single group of muscles. The apparatus consists of two parts, a fixing board and a carriage with tracing apparatus mounted on a suitable frame. The arm is fastened firmly to the fixing board, allowing free movement to only the middle finger of the right hand. To this finger a cord is fastened which, passing to the carriage and over a pulley at the end of the stand, is attached to a weight. In each case in these tests this weight was 7 per cent of the weight of the individual. In flexing the finger the weight is lifted and on extending the finger the weight returns to its original place. A pen attached to the carriage and resting upon a kymograph traces the movement thus made upon paper fastened to the revolving cylinder of the kymograph, and a moving tapeline measures the distance which the weight has been lifted. This distance, multiplied by the weight, gives the amount of work done. By keeping time with the beating of a metronome these flexions and extensions of the finger are made at regular intervals, so that in ninety seconds, the time employed in each test, the weight would be lifted 45 times. In operating the ergograph loaded thus with 7 per cent of the gross weight of the individual it was found that at some period between ninety and one hundred and fifty seconds such fatigue was usually produced as to render it impossible to move the weight at all. By limiting the work to ninety seconds a point was reached at which the strongest pupils would begin to show fatigue, and only the weakest and very obese pupils became entirely exhausted. Table I shows the development of endurance, as shown by the power to do work on the ergograph. It appears that boys have greater endurance than girls at all ages, and during adolescence the differentiation of the sexes becomes very striking. The comparison of the records an individual makes in endurance and vital capacity seems to show that they usually develop together.

THE RATE OF ANNUAL INCREASE IN GROWTH AND DEVELOPMENT.

Table IV shows separately for each sex and for each of the physical measurements taken the following points: First, the special measurement under consideration at the

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