PRECIPITIN TEST

Precipitins are formations in the blood of an animal induced by repeated injections into its veins of the blood-serum of an animal of another species; and their importance in diagnosis lies in the fact that when the blood-serum of an animal so treated is mixed with that of any animal of the second species (or a closely related species) and the mixture kept at a temperature of about 98 degrees for several hours, a visible precipitate will result, but not so if the second ingredient of the mixture is drawn from an animal of an entirely different species. In medico-legal practice, therefore, a suspected ” stain or clot having been first tested by other methods and demonstrated to be blood, the question whether it is the blood of a human being or of other origin is resolved by mixing a solution of it with a quantity of blood-serum taken from a rabbit or some other small animal which bas been previously prepared by injections of human blood-serum. After treatment as above described, the presence of a. precipitate will furnish strong presumptive evidence that the blood tested was of human origin. The test is not absolutely conclusive, for the reason that blood from an anthropoid ape would produce the’ same result, in this experiment as human blood. But if the alternative hypothesis presented attributed the blood in question to some animal of an unrelated species (as, a dog, sheep, or horse) the precipitin test could be fully relied on, as also in the case where no precipitate resulted.