Factors affecting the measurement of absorption bands

Abstract
In a previous paper a method was described by which the percentage saturation of hæmoglobin with carbon monoxide can be estimated. This was done by measuring with a special spectroscope the position of the absorption bands of a solution of blood, since it was found that a definite relationship exists between the percentage saturation with carbon monoxide and the wavelength of the bands. The principle used in the instrument was one first discovered by Zöllner in 1870 and called by him the reversion spectroscope. Two adjacent reversed spectra were obtained by passing beams through a slit suitably placed in relation to a reflecting prism and a replica diffraction grating, optical means being employed for shifting one of the spectra laterally, so that corresponding points in the spectra might be adjusted into line. Since first describing the method I have been able to investigate more thoroughly its accuracy both in my own hands and also in those of other observers. Two different classes of phenomena will receive attention, both of which tend to introduce complications in the use of the method when absolute values for the percentage saturation with carbon monoxide are required. These are:— ( a ) Variations in wave-length determinations made from time to time by same observer on different samples of blood (personal variation). ( b ) Variations in wave-length determination by different observers on same sample of blood (individual variation).

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