Clinical medicine is dependent on certain "normal" standards of comparison for assistance in the diagnosis of many disorders. Body temperature, heart rate, respiration rate, gastric acidity, urinary output and basal metabolic rate afford illustrations of some of the factors that enter into consideration here. Consequently it has become of the greatest practical importance to secure well established standards and likewise readily applicable methods of diagnostic analysis. Appreciation of digression from the normal obviously depends on recognition of what is represented by the latter state. Frequently, if not always, the "normal" is represented by a range of values rather than by any fixed figure or unvarying unit. Circumstances well within the possibilities of good health may give rise to variations within perhaps narrow yet not negligible limits. Environmental conditions, seasons, regimen, age or sex may introduce modifying factors that need to be taken into account before abnormality is postulated.
NORMAL BLOOD COUNTS. JAMA. 1927;88(26):2037. doi:10.1001/jama.1927.02680520027014