182 IMMUNOLOGY 



agglutinable factors distributed among the four blood groups. 

 They found at that time no normal agglutinins in human sera 

 corresponding to these three factors which they designated as 

 M, N, and P agglutinogens. Subsequent studies have shown the 

 M factor to be strictly defined whereas the property P is not. 

 In regard to the latter, they make the following statement, "thus 

 the property P is not strictly defined like A, B, or M, but desig- 

 nates a group of related agglutinable factors." In regard to the 

 N factor they say (July, 1929) that it, like P, shows fluctuation 

 but not to the extent of the latter. Landsteiner and Levine 

 (February, 1929) studied the distribution of these factors among 

 the four blood groups of both white and colored individuals. They 

 found the M agglutinogen present in 80.9 per cent of white and 

 71.9 per cent of colored individuals examined. The distribution 

 among the four blood groups is quite uniform. The N factor 

 is likewise uniformly distributed among the groups and shows 

 the same incidence in botli colored and white individuals. Land- 

 steiner and Levine found it present in 73.9 per cent of the white 

 and 72.4 per cent of the colored individuals examined by them. 

 In regard to the P factor they state, "The strongest reactions 

 were almost four times as frequent in the colored as in the white 

 individuals, whereas the weak reactions were much rarer in the 

 former. Blood with negative reactions occurred only exception- 

 ally among the colored." 



Landsteiner and Levine (1928) have shown that M and N fac- 

 tors are inherited as Mendelian dominants, probably dependent 

 upon a single pair of allelomorphic genes M and N. The resultant 

 possible types are M, N, and MN. These factors occur as ag- 

 glutinogens demonstrable only by immune serum. These immune 

 sera are usually prepared by the injection of known J\I and N 

 blood cells into rabbits. Recent work (Stuart, et al., 1936, 1937, 

 1939) has shown that rabbits, in order to produce potent antibodies, 

 must not contain M factors in their tissues. Studies on the dis- 

 tribution of these factors show that M and N occur regularly in 

 human cells but are independent of the A and B factors. They 

 may be used in medico-legal work in tlie same way as the A and B 

 factors. However, by the determination of M and N as well as 

 A and B the average chances of proving nonpaternity are doubled. 



