Should the stain suspected be other than human, and derived from one of the other animals used for antiserum in stand B, then the positive reaction will occur in the particular tube.[12] The test is now recognised as very sensitive and reliable, and is also applicable to the detection of the flesh or fluids of animals, and has thus been used for the detection of meat stuffs.
Tarchetti advises the following procedure in the examination of blood-stains: Dissolve the stain in a few drops of a 0.9 per cent. aqueous solution of sodium chloride, filter, and divide the filtrate into two portions; to one (a) add 0.5 c.c. of the prepared rabbit serum (the so-called antiserum); to the other (b) serum from a rabbit which has not been injected with human blood. Both are to be placed in an incubator at 37° C. for an hour. By this time, if the solution of the stain be of human or anthropoid origin, the contents of the tube (a) will have become turbid, the contents of tube (b) will remain clear. From a series of experiments with blood-stains of man and other animals on a variety of materials, Tarchetti states that this method is reliable. Prepared rabbit “human antiserum” has been shown to have no such reaction with the blood of the pig, ox, calf, mouse, or rat.
From the result of his investigations Grünbaum points out that these reactions must be looked upon rather as “special” than “specific,” in view of the fact that his “chimpanzee antiserum” gave a slight but distinct turbidity after a few hours with horse blood. He also suggests a method for the microscopical application of the “biological test,” by using a 1 per cent. blood solution with a drop of “antiserum.” This method has enabled him to distinguish between human and anthropoid blood, the reaction occurring earlier and being more complete when the “antiserum” is used on its own blood.
Vegetable and other Stains
which resemble Blood
Certain vegetable colouring matters give spectra which may be mistaken for blood, from their close similarity. Of these cochineal dissolved in a solution of alum gives two bands similar to O₂Hb. On the addition of boric acid the bands move to the violet end of the spectrum, but they are unaffected if the colouring matter be blood. Lac-dye, alkanet root, madder, and others also give spectra resembling O₂Hb, but they are changed or disappear on adding ammonia or sulphite of potassium, while the spectrum of blood remains unaltered.
As stated previously, spectra of colouring matters other than blood are not capable of being altered by reducing agents, so that, however similar they may be to O₂Hb, they cannot be accepted as derived from blood unless the spectra of reduced Hb and reduced hæmatin can be obtained in the way described.
Cochineal, colours of certain roots and wood, turn crimson on the addition of ammonia, logwood bluish-black.
The colour of the rose and certain flowers turn green on adding ammonia.
Fruit-stains from mulberry, currants, gooseberries, &c., turn bluish-green with ammonia.
Vegetable stains have their colour heightened by the action of dilute acids.