Ill] ADOLPHE QUETELET 89 



capable of very different rates of increment. The changes of form 

 which result from these differences in rate are especially manifested 

 during that phase of life when growth itself is rapid: when the 

 organism^ as we say, is undergoing its development. 



When growth in general has slowed down, the differences in rate 

 between different parts of the organism may still exist, and may be 

 made manifest by careful observation and measurement, but the 

 resultant change of form is less apt to strike the eye. Great as are 

 the differences between the rates of growth in different parts of a 

 complex organism, the marvel is that the ratios between them are 

 so nicely balanced as they are, and so capable of keeping the form 

 of the growing organism all but unchanged for long periods of time, 

 or of slowly changing it in its own harmonious way. There is the 

 nicest possible balance of forces and resistances in every part of 

 the complex body; and when this normal equilibrium is disturbed, 

 then we get abnormal growth, in the shape of tumours and exostoses, 

 and other malformations and deformities of every kind. 



The rate of growth in man 

 Man will serve us as well as another organism for our first illus- 

 trations of rate of growth, nor can we easily find another which we 

 can better study from birth to the utmost Hmits ofold age. Nor 

 can we do better than go for our first data concerning him to 

 Quetelet's Essai de Physique Sociale, an epoch-making book for the 

 biologist. For it is packed with information, some of it unsurpassed, 

 in regard to human growth and form; and it stands out as the 

 first great essay in which social statistics and organic variation are 

 dealt with from the point of view of the mathematical theory of 

 probabilities. How on the one hand Quetelet followed Da Vinci, 

 Luca Pacioli and Dlirer in studying the growth and proportions of 

 man : and how on the other he simplified and extended the ideas of 

 James Bernoulli, of d'Alembert, Laplace, Poisson and the rest, is 

 another and a vastly interesting story*. 



* Quetelet, Sur V Homme, ..., ou Essai de Physique Sociale, Bruxelles, 1835: 

 trans. Edinburgh, 1842; a,\so Instructions populaires sur le calcul des probabilites, 1828; 

 Lettres. . .sur la theorie des probabilites appliquee aux sciences morales et politiques, 

 1846 ; and Anthropometrie, 1871 . For an account of his life and writings, see Lottin's 

 Quetelet, statisticien et sociologue, Louvain, 1912; also J. M. Keynes. Treatise on 

 Probability, 1921. 



