Any excess of stain should be removed by washing in distilled water, and the specimen allowed to drain by standing it on edge upon a piece of filter paper; it should then be allowed to dry, and then counterstained with a freshly prepared aqueous solution of methylene blue, hæmatoxylin solution, or other nuclear dye. Wash again in distilled water, allow to dry, and mount in Canada balsam. By this method the corpuscle will be stained pink, and if nucleated, the nucleus will be stained by the methylene blue, hæmatoxylin, or other nuclear stain which may have been used.
Leishman‘s stain may be used. This stain being a methyl-alcohol solution is used for fixing and staining at the same time. A few drops of the stain is placed on the dried film; after standing until evaporation is almost complete, distilled water is dropped on to the slide, and left to stand for two or three minutes, it is then drained off, and a few more drops of distilled water added until the film is pink in colour, then dried with filter paper. Red corpuscles are tinted red with the eosin, and nuclei of leucocytes or nucleated red cells violet or deep blue. The specimen may be examined direct with the oil immersion or mounted in Canada balsam.
When examining specimens prepared from blood-stains, it is necessary to search carefully for other cellular structures such as epithelial cells, spermatozoa, or fragments of hair.
It may be advisable, in certain cases where the amount of material submitted for examination is small, to centrifugalise some of the solution in a fine glass tube, in order to determine any cellular elements present to one spot. By making use of this concentrated portion containing the cellular elements for the preparation of a microscopic specimen, one not only facilitates the microscopical examination, but is able to place more reliance upon the results obtained.
The Results of Microscopical Examination of
Blood-Stains in Their Medico-Legal Relations.
As previously stated, the examination of alleged blood-stains from a medico-legal standpoint is pursued essentially for the purpose of testifying as to whether they have been produced by blood or not. Where the examination yields a negative result, further procedure is necessary with a view of identifying the true nature of the stain. Should, however, the result be positive, the question arises as to the possibility of distinguishing between human blood and the blood of other animals, and determining the exact animal from which the blood has been derived. Such an examination should be pursued in full recognition of its importance as a factor towards the establishment of truth essential to the administration of justice.
To fulfil this obligation the methods employed should be so selected as to produce results bearing testimony free from any possibility of doubt.
Certain differences exist, and may be detected by microscopical examination, between the red corpuscles of human blood and those of some other animals sufficiently well marked to render differentiation possible. The differences are those of form and structure.
(1) In man the red corpuscles appear as circular biconcave discs, averaging ¹/₃₅₀₀ of an inch in diameter, and are non-nucleated.
The red corpuscles of mammals present the same features, with the exception of the