[48] _Untersuchungen von Blutspuren_ in Maschka’s _Handbuch_, Bd. i. Halfband 2. § 35. =Spectroscopic Appearances of Blood.=--If defibrinated blood[49] be diluted with water until it contains about ·01 per cent. of oxyhæmoglobin, and be examined by a spectroscope, the layer of liquid being 1 centimetre thick, a single absorption band between the wave lengths 583 and 575 is observed, and, under favourable circumstances, there is also to be seen a very weak band from 550 to 532. With solutions so dilute as this, there is no absorption at either the violet or the red end of the spectrum. A solution containing ·09 per cent. of oxyhæmoglobin shows very little absorption in the red end, but the violet end is dark up to about the wave length 428. Two absorption bands may now be distinctly seen. A solution containing ·37 per cent. of oxyhæmoglobin shows absorption of the red end to about W.L. 720; the violet is entirely, the blue partly, absorbed to about 453. The bands are considerably broader, but the centre of the bands occupies the same relative position. A solution containing as much as ·8 per cent. of oxyhæmoglobin is very dark; the two bands have amalgamated, the red end of the spectrum is absorbed nearly up to Fraunhofer’s line a; the green is just visible between W.L. 498 and 518. Venous blood, or arterial blood, which has been treated with reducing agents, such, for example, as an alkaline sulphide, gives the spectrum of reduced hæmoglobin. If the solution is equivalent to about ·2 per cent., a single broad band, with the edges very little defined, is seen to occupy the space between W.L. 595 and 538, the band being darkest about 550; both ends of the spectrum are more absorbed than by a solution of oxyhæmoglobin of the same strength. In the blood of persons or animals poisoned with hydric sulphide--to the spectrum of reduced hæmoglobin, there is added a weak absorption band in the red, with its centre nearly corresponding with the Fraunhofer line C. Blood which has been exposed to carbon oxide has a distinct spectrum, due, it would seem, to a special combination of this gas with hæmoglobin; in other words, instead of oxygen, the oxygen of oxyhæmoglobin has been displaced by carbon oxide, and crystals of carbon oxide-hæmoglobin, isomorphous with those of oxyhæmoglobin, may be obtained by suitable treatment. The spectrum of carbon oxide-hæmoglobin, however, differs so little from that of normal blood, that it is only comparison with the ordinary spectrum, or careful measurements, which will enable any person, not very familiar with the different spectra of blood, to detect it; with careful and painstaking observation the two spectra are seen to be distinct. The difference between the carbon oxide and the normal spectrum essentially consists in a slight moving of the bands nearer to E. According to the measurements of Gamgee, the band α of CO-hæmoglobin has its centre approximately at W.L. 572, and the band β has for its centre W.L.