DEVELOPMENT AND GROWTH OF HEMATOPOIETIC TISSUES

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Abstract
1. Growth in body weight, organ weight, volume, or number of cells is better described over long periods of time by a straight line on log log paper than on arithmetic or semilog paper. 2. A most useful form of the equation describing these straight lines is [see equation in source pdf] where y = any measured variable and t = time from fertilization in prenatal life, and from birth in postnatal life. [see equation in source pdf] or the slope of the straight line. 3. The advantages and disadvantages of this equation are presented. Among its chief advantages are: the fact that the semilogarithmic plot, because of the steadily increasing doubling time, cannot be a good model; the advantages of a straight line over a complex curve; the fact that readable values are obtained over factors of as much as one millionfold increases in values; that the scales are easy to read in the periods of most rapid growth; that the equation is independent of the units or the base of the logarithms used; that the ratios of the exponent x can be used in allometric studies; and, that equidistant parallel lines describe the range of distribution of individual data from the logarithmic mean or median. Its disadvantages, which apply to all other equations of growth equally, are that it does not express the true complexity of the growth processes nor the extreme readjustments that occur in the first few days after birth. 4. Growth in body weight of the fetus and child, and of the organs and cells of the hemic system are presented more as examples of a method of analysis, which should lead to better data in the future than as final standards. 5. The qualitative development of the hematopoietic system in the early fetal period is outlined. 6. The first data on the number of cells in the human fetus are given. 7. Particularly interesting observations are: the constant values for lymphocytes during most of childhood; the approximately equal numbers of the non-nucleated and nucleated cells in the fetus; the consistent change in growth rate between 7 and 8 years; and the relatively constant total hemoglobin in postnatal life at 1 per cent of body weight. 8. The simplicity and clinical usefulness of this method of analysis of growth data suggests that it could well be used in the practice of every pediatrician and in many types of research. 9. The methods employed should be equally applicable to other species and to the growth of many tumors. 10. This equation and method of growth analysis take into consideration the relativity of biologic time.

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