BIOLOGICAL VARIATION AND QUANTIFICATION OF HEALTH - THE EMERGENCE OF THE CONCEPT OF NORMALITY

Historical research on the concept of normality, its roots and its dev elopment show that this concept has its sources in very different area s of scientific and medical thinking. Of great importance were: (i) a new theory of disease arising early in the 19th century supposing a co ntinuous change from the healthy to the diseased state; (ii) the exami nation of variation within and between species of plants and animals; (iii) the clinical theory of constitution developed to describe the wh oleness of the individual determined both by genetic factors and the i nfluence of the environment; (iv) the development of mathematical and statistical tools starting with the adaptation of Bernoulli's ''law of the great numbers'' and Gauss' and Legendre's ''law of errors'' to bi ological measurements by the Belgian astronomer Quetelet. At the end o f the First World War the concept of normality was first discussed. An idealistic ''value norm'' was set against a statistical ''frequency n orm'' Between 1920 and 1930 the principles of our present concept were accepted and the mathematical tools developed. It took several decade s to introduce this concept into practical medicine finally being reco mmended by the IFCC.