December 13, 1912] 



SCIENCE 



817 



cussion of Professor Porter's observations on 

 the growth of school children in St. Louis, I 

 pointed out the fact that a general variability 

 in physiological development accounts for the 

 close correlation betveeen the distribution of 

 ages in school grades and the size of the body 

 and its organs; and this problem was later on 

 worked out by myself in conjunction with Dr. 

 Clark Wissler in regard to various measure- 

 ments. These correlations have also been 

 proved in a most interesting manner by Dr. 

 Crampton's observations on pubescence, and 

 by Professor Eotch's and Pryor's study of the 

 development of the epiphyses and carpal bones. 

 It is true that a close correlation between the 

 status of the physiological development of the 

 various parts of the body exists, but there 

 exists also a certain amount of variability in 

 the development of an organ when another one 

 has reached a definite stage. The correlation 

 is so close that the condition of the bones or 

 that of pubescence gives us a better insight 

 into the physiological development of the indi- 

 vidual than his actual, chronological age, and 

 may therefore be advantageously used for the 

 regulation of child labor and school entrance, 

 as Roteh and Crampton advocate ; but we must 

 not commit the error of identifying physiolog- 

 ical development with physiological age, or of 

 considering chronological age as irrelevant. 

 The clearest proof that is available is found in 

 the data relating to increase of stature, and 

 in observations on pubescence made according 

 to Dr. Crampton's methods. Bowditeh was 

 the first to investigate the phenomena of 

 growth of individuals who are short or tall 

 at a given age, but his method was based on a 

 statistical error. Later on I showed that re- 

 tarded individuals possess a late acceleration 

 of growth, and these results were amplified by 

 studies made by Dr. Beyer and Dr. Wissler. 

 Eecently I had occasion to make a more de- 

 tailed statistical analysis of the phenomena of 

 growth, which show that individuals whose 

 prepubertal accelerated grovrth begins late in 

 life have rates of gTowth that exceed by far 

 those of the normal individual ; in other words, 

 that among the retarded individuals the whole 

 energy required for growth is expended in a 



very brief period. In the case of stature the 

 phenomenon is complicated by the great differ- 

 ences in hereditary stature among the various 

 parts of the population. It appears more 

 clearly in observations on pubescence. The 

 observations indicate that if the first pubic 

 hair appears in one group of boys at eleven 

 and a half years, in another at fifteen and a 

 half years, it will take the former much longer 

 than the latter to attain the full development 

 of pubic hair, and the rate of change found 

 among them will be much greater than that of 

 normally developed individuals. Although 

 further data are required to determine this 

 point definitely, it is certain that we must not 

 assume that individuals who exhibit the same 

 stages of physiological development are the 

 same, physiologically speaking, no matter what 

 their actual age may be; on the contrary, the 

 past and prospective physiological changes in 

 their bodies will proceed in different manners. 

 It is clear, therefore, that the greater the re- 

 tardation or acceleration in any one particular 

 respect, the greater will also be the dishar- 

 monies that develop in the body, since not all 

 the other organs will follow the same rate of 

 acceleration and retardation. 



The causes of these phenomena are un- 

 known; but we may perhaps venture on the 

 hypothetical explanation that all the cells of 

 the body undergo certain progressive changes 

 with increasing age, and that the internal 

 secretions which become active at the time of 

 puberty exert a stimulus upon the cells which 

 causes accelerated growth in the cells, and 

 that the intensity of this influence depends also 

 upon the state of development of these cells. 

 This may refer to the whole body as well as 

 to the glands that have a direct influence upon 

 the rate of growth. In retarded individuals 

 many of the cells have advanced in their de- 

 velopment more nearly normally than the 

 groups of cells involved in sexual maturity; 

 and when their action sets in, the cells of the 

 body are stimulated much more vigorously 

 than the less developed ones of an individual 

 that reaches maturity at an earlier time. This 

 hypothesis, however, would have to be tested 

 experimentally. It is intended only to bring 



