BLOOD TESTS

Evening Star, Issue 19776, 28 January 1928, Page 18

BLOOD TESTS

AS mvmi OF PATEBBUY msm E3 OF TBAKSFUSHH! BLOODS THAT WILL NOT MIX. The use of blood tests to determine paternity is illustrated by two legal cases reported from Germany (writes the medical correspondent of the London ‘Observer’). The first was heard in Wurttomherg, where a woman applying for an affiliation order swore that a, certain man was the father of her illegitimate child. The defence countered by producing evidence that the characteristics of the infant’s blood were incompatible with this relationship. The blood of the man, they said, was of one type, and the woman’s was of another; it was impossible that the union of two such persons could have produced offspring whose blood had the characteristics demonstrated. By which reasoning the court was so far convinced as to sentence the woman to six months’ imprisonment for perjury. The second case was of the same kind, but the judgment delivered on it by the highest Prussian Court was in a contrary sense. Simliar medical evidence was brought to refute a charge of paternity, and the general validity of the blood tests was admitted. Apparently, however, a witness stated_ in a series of over 2,0U0 cases investigated in 192 G there had been one exception to the rule, and the court accordingly decided that the tests do not provide the absolute proof required by the law. INCOMPATIBILITIES. Before commenting on these judgments it is convenient to consider the origin and nature of the new tests, whose use for legal purposes is no more than adventitious.

They have arisen as a by-product of the operation known as blood transfusion—that is to say, the transference of blood from the veins of one individual to those of another. After sudden hreinorrhage and in many forms of disease such reinforcement is of great value, and has been from time to time attempted by surgeons for hundreds of years. But the technical difficulties have always been considerable, and even when they had been overcome it was still found that the operation sometimes caused dangerous symptoms—such as shock and unconsciousness—and even sudden death. Thus it came to be realised that the blood of some human beings is incompatible with that of others, producing a violent and dangerous reaction if injected into the body. Although blood appears homogeneous, it really consists of discrete corpuscles floating in an almost colorless fluid known as serum. It is easy to separate these two constituents, and it was found that if a drop of serum from one person was added to a drop of blood from another, the conjunction sometimes caused the corpuscles to run together in clumps. To this “ agglutination ” the poisonous effects of transfusion Avere evidently due, and it became the practice, before starting the operation, to make sure that the bloods of the two individuals concerned did not show this antagonism to each other under the microscope. CLASSIFICATION OF BLOOD.

Even simpler means of preventing accidents are uoav, hoAvever, available; for it has been discovered that the blood of all human beings falls into one of four groups. The tests Avhicli define these groups depend on a theory that human blood corpuscles may contain one or both of tAvo substances, called A and B. Similarly, human serum may contain one or both of tAvo substances, “a” and “b.” It is impossible for A and “a” to coexist in one individual, for the result of their meeting is agglutination of the blood corpuscles—a phenomenon Avhich also occurs Avhen 11 b ” meets B. Thus there are four possible types of blood, kuoAvn as groups L, 11., m., and IV.. containing A plus B, “Aphis ‘‘b,’ a plus B, and “a” plus “b” respectively. , , , ■ , A person s group can bo ascertained by putting two drops of his blood at opposite ends of a glass slide and adding “a ” (scrum from group III.) to one and “ b” (serum from group II.) to the other. Within a few minutes show clumping of the corpuscles, and one, both, or neither of the drops avill slioav clumping of the corpuscles, and will thus reveal the group to which their owner belongs. It, may be remarked in passing that the evil effects of transfusion only occur when the corpuscles of the donor are susceptible of agglutination by the serum of the recipient—;.e., the patient whose blood is being supplemented. This means that the blood of people in group IV. (who comprise some 40 per cent, of the population) can safely be transferred to anyone, of whatever group. A roll of these “ universal donors ” is kept at hospitals, so that they ran be called on to give their blood in an emergency Avithout further investigation. VALUE OF THE TESTS AS EVIDENCE. One medico-legal application of these tests is to the examination of bloodstains, for it can sometimes bo shown that the blood from a given stain could not have been shed by the person to Avhom it is attributed. Their use to refute allegations of paternity is not so simple, since it depends on our knoAvledge of the Avay in which the characteristics of the blood are _ inherited. The available evidence indicates that A and B are “ dominant ” characters, Avhilst “a” and “b” are “ recessiA'e.’’ On this assumption A and B can never be found in the blood of a child unless they are present in that of the father or the mother. For instance, a child who belongs to group 11. cannot have sprung from tAvo group IV. parents. In Austria the tests have been accepted in the law courts for more than a year, and a number of men who bad been paying for the support of their alleged children have had their cases reopened, and by this hind of evidence haA'e made good their denial of paternity. Without knoAving more about the “exceptional” case Avhicb _ influenced the Prussian judges in their decision, it is impossible' to assess its significance. The tests are believed to rest on a sound foundation and _to be reliable within the limits indicated;/ but. ns the ‘ Lancet ’ points out, the British courts do not nhvays accept the_ most definite scientific evidence Avitbont reservation. Even proof of identity liy finger-prints, though used by the police for purposes of detection, is seldom invoked in order to secure the coiaa'iction of a criminal.