Insufficient or excessive feeding has a considerable influence on the body weight; for instance, if poor city children enter fresh air colonies, their weight increases considerably during the few weeks they live in the country and receive an abundant supply of food, but frequently they lose this gain after returning to their former life. Manifestly such a gain is more a matter of fattening them than an expression of growth. Frequently we find such an overnutrition in cases of sucklings, many of whom do not progress very well with their general development in spite of their great weight, and who lose their excessive weight when, for in stance, they pass from the excessive milk diet to the table food.
The length is also subject to certain variations, but these cannot be demonstrated as easily as can the variations of the weight. Children and adults are 1 to 3 cm. longer immediately after the night's rest in bed, than a few hours later. In case of great fatigue the length of the body may be shortened as much as 4 to 5 cm.
If we consider that for several years the total yearly increase in length is only 5 cm., measurements disregarding these variations may lead to very erroneous results. The daily decrease in length does not proceed regularly during the day, but is subject to continual variations. The decrease begins. immediately after rising and reaches its maximum about four to five hours later. After lying for sonic time in a horizontal position (in the afternoon, for instance), the body regains its maximal length. The variations are mainly caused by the following circumstances: The erect position leads to a compression of the cartilaginous layers between the single the spinal column becomes curved, and the vault of the foot becomes depressed. A more pronounced erect posi tion increases the length a little, and most recruits are therefore a little longer after a short time of service. But all this has nothing to do with growth in a more restricted sense, just as little as has the increase of length in the case of children who have been kept in bed on account of disease.
The exact determination of the length is difficult in itself, and, par ticularly in the case of infants, is very much more complicated than the determination of the weight. An excellent observer, the late Professor Wiener, found differences amounting to 3 min., measuring repeatedly within short intervals; observers of less skill will easily make errors of from 0.5 to 0.7 cm., even if their method is good.
Beside the daily variations of weight and length, there are regular variations in the course of the seasons, and these are not connected in any way with the growth. The greatest gain in weight in the course of the year occurs in the Fall, from August to December; the smallest gain is registered during the Spring, from April to July. The increase in length is exactly reversed.
Many factors, therefore, have to be considered if we want to determine the weight and length of the body, and to use the results obtained for the determination of the growth. The weighing should
be done in the morning before any food is given, and without any clothes, or with as little clothing as possibl, and the length should be measured in the morning immediately after leaving the bed.
It is desirable to obtain reliable average values from observations on a larger number of children, since the weighing and measuring of a given case may be subject to accidental mistakes. Such values are indis pensable for the physician and hygienist. Two different methods may be employed in order to gain these average values, the generalizing, or method of collective. investigation, and the individualizing. Using the first method, numerous children of about the same age (for instance, members of a class in school) arc weighed and measured to form an average value for a given age. In this way it is possible to obtain values of weight and length for the total period of growth within a short time. It can readily he understood that this method cannot give satisfactory results if the material of observation is not absolutely uniform. Age and sex, the race, social condition, state of health, time of year and day, etc., must be taken into consideration most carefully. Using the second method, the weight and length of single individuals are determined dur ing the total period of development, and by combining numerous such observations in a suitable manner we arrive at average values. This laborious and tedious method must be adopted if we want to gain information about the finer processes of growth. While the collective investigation reduces or annuls the influence of accidental variations, it effaces at the same time regular variations and influences, the knowl edge of which is desirable and necessary. For instance, during the first year of life the expected influence of teething and weaning can only he elicited from observations on the single individual. By weighing several infants five months old, others six months old, and again others seven months old, we can obtain the average weight for the given age. But the influence of teething and weaning is entirely effaced, because these events do not occur in all these infants at the same age, but in one case in the fifth. in the other in the sixth month. Using the generalizing method, we can make certain subdivisions in order to study the effect of special influences, those of wealth and of poverty, for instance. But the subdivision is made here before the observations are taken and according to a preconceived idea. Using the individualizing method, we can make suitable subdivisions on the basis of the results obtained by observations on single individuals, remembering that these results will be conditioned by the degree of uniformity in the material. Therefore, this latter method furnishes the best results, since it enables us to observe the growth of the individual and to arrive at suitable average values.