98 MEDICAL JURISPRUDENCE gens (isogens), A and B, and the blood serum contains two homologous factors (agglutinins), designated as iso-haemagglutinins (isonins), a and b. These iso-hsemagglutinogens may occur in a blood either singly or together, or they may not occur in blood at all. The same is the case with the presence of iso-haemagglutinins in a blood. These agglutinogens and agglutinins are permanent and persist in the blood throughout life without any change. They are not affected by disease and environmental conditions and are independent of sex and age. The agglutinogens are almost always pfesent at birth, but the agglutinins which are to characterize the individual through- out life are present in only about half of the newly-born infants. These are believed to have been derived from the mother's blood by filtration through the placenta. The agglutinins which are present at birth diminish or dis- appear during the first ten days of life ; after this the infants produce their own agglutinins according to their own blood groups. There is some difficulty about the classification of these groups. Moss has modified Jansky's classification by reversing groups I and IV, and retaining the position of groups II and III. To avoid this confusion a new international nomenclature based on the agglutinogen content of ' the red "blood corpuscles has been adopted by the Health Committee of the League of Nations, and the four blood groups are now referred to as O, A, B, and AB, where O represents the absence of the iso-haemagglutinogens and A and B, the presence of the same. Greval and his collaborators have designed a diagram which illustrates well the distribution of the iso-haemagglutinogens in the red blood corpuscles and the iso-hsemagglutinins in the serum and also explains the equivalents in the old and new nomenclatures of the blood groups 24 (see Plate II). Two more haemagglutinogens (not iso-hsernagglutinogens), known as hsemogens M and N, which are quite unrelated to A and B, occur in the red blood corpuscles, and either M, N or MN type is present in the red blood corpuscles of all human beings. These haemagglutinogens are present at birth and remain constant throughout life. The hsemagglutinins cor- responding to the M and N haemagglutinogens (haemogens) do not occur in the human sera; hence the presence of the M and N hsemogens can only be demonstrated by immunizing a rabbit with the red blood corpuscles which contain the pure M or N hsemogen and by using the serum thus obtained to test out the unknown corpuscles. It is possible that by the help of the M and N hsemogens the four classical "blood groups may be further sub- divided into twelve distinct types, viz. OM, ON, OMN, AM, AN, AMN, BM, BN, BMN, ABM, and ABMN. If sub-groups with AI and Ao are also considered, there will be eighteen distinct types. The following table25 gives the percentage of the individuals in each group and also the percentage of the type occurring in the groups as ob- tained from the examination of the bloods of 300 Indians in Calcutta hospitals by Greval, Chandra and Woodhead : — Groups. Types. M N MN Per cent 0 26.7 A 26.7 B 37.7 AB 9 Per cent 41.2 38.7 45.1 48.1 Per cent 12.5 13.7 9.7 0 Per cent 46.2 47.5 45.1 51.8 24. Greval, Chandra and Woodhead, Ind. Jour. Med. Res., April 1939, p. 1,042; Ind. Jour. Med. Res., Jan. 1941, p. 231. 25. Ind. Jour. Med. Res., April 1939, p. 1,048: For distribution, of blood groups in a Madras population vide Sheshadrinathan and Timothy, Ind. Jour. Med. Res.3 July 1942, p. 445.