142 LIFE: ITS NATURE AND ORIGIN 



The envelopes of erythrocytes have areas of what appear to be 

 specific polysaccharide substances which act as agglutinogens and can 

 react with corresponding agglutinins. K. Landsteiner's pioneer work 

 (1900-1) has been extended, and there are now recognized, in humans, 

 the following types: A, B, AB, O; subgroups of A and AB; the M. N, 

 and P agglutinogens of K. Landsteiner and P. Levine ; and the Rh 

 factor of K. Landsteiner and A. S. Wiener. 7 These agglutinogens can 

 be distinguished by tests with suitable antisera prepared by immunizing 

 human beings or animals. Agglutination generally occurs, but in 

 some cases hemolysis of the red blood cells takes place. A. S. Wiener 

 states: "In place of the original, single Rh factor, transmitted by a 

 pair of allelic genes, Rh and rh, three Rh factors are known at the 

 present time, together with a so-called Hr factor, and these, in com- 

 bination, give rise to a large series of different varieties of Rh agglu- 

 tinogens, determined by a corresponding set of at least ten or more 

 allelic genes." 8 In fact, all the different "blood groups" seem to be 

 distributed genetically, and the bloods of animals close together on the 

 phylogenetic scale, (for example, man and chimpanzee, rat and mouse) 

 are immunologically related. If a goat is immunized by injections of 

 red blood cells of man, rabbit, and pigeon, the blood cells of each of 

 these three animals will absorb from the goat's serum only its own 

 specific agglutinin. 



The immunological consequences arising from differences in 

 blood groups have much to do with incompatibility of blood used 

 in making transfusions, so that a suitable blood donor must be 

 selected. In plasma transfusions, blood group differences can 

 usually be disregarded. Transplantations of tissues may also fail 

 because of such or similar incompatabilities. In some cases this 

 may cause the death of a child in utero, or shortly after birth 

 (Erythryblastosis fetalis), unless the blood of the infant which has 

 been damaged by the maternal antibodies, can be replaced soon 

 enough by compatible blood. 



Embryonic and new-born animals usually have passive immu- 

 nity to certain antigens, acquired by diffusion of parental anti- 

 bodies through the placenta, or else by their deposition in the 

 egg. Embryos and young are able to form antibodies very 

 slightly, if at all; and before the new-born animal develops this 

 power and thus establishes its own active immunity, its passive 

 immunity begins to drop off. Hence the very young are generally 

 susceptible to many antigens, especially to the viruses and bacteria 

 of "children's diseases." 9 Passive immunity is now commonly 

 given children by injections of antibodies, of antigen-antibodies, 



