104 MEDICAL JURISPRUDENCE It may be necessary to determine the group of a blood stain in a crimi- nal case where a stain detected on the person or clothing of an accused is found to be due to human blood, but the defence counsel may suggest that the blood stain was the accused's own blood as a result of an accident and not that of the victim. A preliminary agglutination test should be carried out, using the fresh red blood corpuscles drawn from the accused and the extract prepared by soaking the blood stain in an appropriate amount of normal saline solution. If there is agglutination of the blood, the stain cannot be that of the accused. If there is no agglutination or if two blood stains are to be compared, the stains should be grouped by testing saline extracts for the agglutinins a and b, using two sets of the fresh red blood corpuscles which are known to contain the iso-hsemagglutinogens A and B respectively. In addition an absorption test should be performed as sug- gested by Alieff.39 If the blood group of the stain be the same as that of the victim, and different from that of the accused, this is an additional piece of evidence of the guilt of the accused. If, however, the accused and the victim are of the same blood group, the test has no medico-legal value. On the other hand, if the stain and the accused be of the same blood group, and the victim of a different group, the test will be of great help in proving the innocence of the accused. It is, therefore, necessary to determine the blood group at the time of the post-mortem examination of the body of the victim in every homicidal case, so that a comparison might be made with blood stains on the weapon alleged to have been used, clothing and person of the accused. Roche Lynch 40 cites a case in which an assailant murdered a young typist by cutting her throat and disappeared, and the razor which was assumed to have been used for cutting the throat was found subsequently on an omni- bus eight or ten hours later. The blood-stained clothing of the deceased girl and the blood stains on the razor were examined, and both were found to belong to Group AB ; hence he concluded that the razor was used in the crime. A case41 is also recorded in which an American coloured soldier was convicted and sentenced to death for strangling a crippled taxi driver at Ipswich on the ground that the blood on the accused's clothing and the blood of the victim were found to belong to Group AB, even though the accused had given evidence that he was in London on the night of the murder and that the blood on his clothing was due to his having had a fight. SUBSTANCES RESEMBLING BLOOD STAINS Certain substances produce beautiful dark or reddish-brown stains, especially on clothes, which resemble fresh and old blood stains very closely. The most important of them are rust or iron mould stains, red synthetic dye stains, stains caused by red paints of mineral origin and stains of vegetable origin produced by certain fruits, flowers, leaves, barks and roots. Rust Stains.óRust stains on knives and steel weapons often look like dried blood stains, but they seldom have a dark and glazed appearance and do not fall off in scales, when the other side- of the blade is heated. Similarly, rust stains or iron mould stains on linen may present the appearance of old dried blood stains, but these stains do not stiffen the cloth. They are reddish- brown in colour and insoluble in water but are soluble in dilute hydrochloric acid. The usual tests for iron, viz. potassium ferrocyanide and potassium sulphocyanide tests, may be employed after oxidizing the stain with a drop of nitric acid if necessary. The addition of glacial acetic acid to the stain 39, Buss kaya, Klmifco, Moscow, 1927, VH, p. 55; Whitley and Briton, Disorders of the Blood, Ed. n, p. 483. 40, Medico-Legal and Criminolooical Review, Anril 1933, t>. 112. 41, Med.-leg, and Criminolog. Rev., 1944, Vol. XII, Part "ll, p. 105.