THE COLORIMETRIC estimation of haemoglobin concentration by reference to a standard of diluted blood was introduced by Gowers in 1878 and, after modification by Haldane in 1901, was widely used until the 1960s. Haldane's "normal" standard was determined by measurement of a very small group of men in Belfast and subsequent work indicated apparent differences between this and the normal level in Britain thirty years later, and also differences between British and American "normal" levels. These

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... fferences are discussed and some possible explanations suggested to account for them. INTRODUCIION At the beginning of the present century the practice of haematology for clinical purposes was effectively restricted to total and differential red cell counts and to simple measurements of coagulation. Haemoglobin concentration was rarely estimated, and measurement of oxygen capacity was a research procedure outside the scope of clinical medicine. Wright was reported as saying that: "In hospitals at the present time, the chief, and in many hospitals the only, method of blood examination which was in use was the haemocytometric method,"' while Lorrain Smith complained that: "The methods in ordinary use for examining the blood of patients suffering from anaemia fail to give any information whatever regarding the total quantity of blood in the circulation, or the total amount of haemoglobin which it contains."2 COLORIMETRIC HAEMOGLOBINOMETRY A colorimetric method for the estimation of haemoglobin was introduced almost a century ago by Gowers,3 who devised an apparatus (Fig.