Spectroscopic Examination
To a portion of the coloured solution, filtered if necessary, the spectroscopic tests should be applied. The following points must be remembered in carrying out a spectroscopic examination:
(a) The colouring matter of fresh blood is hæmoglobin, and it may exist in two states, according to the degree of its combination with oxygen.
In arterial blood it is present as oxidised hæmoglobin, and the same obtains in blood which has been exposed to the air under certain conditions and for a varying period of time.
Fig. 14.—Photo-micrograph of crystals of hæmin, × 250.
(R. J. M. Buchanan.)
In venous blood, especially when obtained under conditions preventing oxidation, as from the heart cavity of an animal newly asphyxiated, it is present as deoxidised hæmoglobin.
(b) In dry stains, especially if they have been subjected to the action of impure air containing the products of coal-combustion, the colouring matter becomes changed into methæmoglobin, or hæmoglobin in which its combination with oxygen has been altered in such a way that a current of a neutral gas, such as hydrogen or nitrogen, will not dissociate it, as it does with oxyhæmoglobin. Such stains have a brownish colour, and may give an acid reaction.
(c) In stains which have retained moisture, from having lain in damp places, the hæmoglobin becomes converted into hæmatin. The same change takes place in dry stains after a longer period of time.
On examining the solution of the colouring matter from a blood-stain with the spectroscope, the spectrum will vary according to its condition and the nature of the solvent used.