BLOOD GROUPS, HETEROGENETIC ANTIGENS 493 



In regard to the time of development of the blood-group differentials and 

 of the corresponding agglutinins in the blood serum, this shows some paral- 

 lelism to the time of origin of the organismal differentials. The experiments of 

 Blumenthal have shown that the latter are not yet fully developed during the 

 first stages of embryonal development, but can be demonstrated during the 

 second half of the intrauterine life of the embryo. From Murphy's experiments 

 on the transplantation of heterogenous tissues to the allantois, and from 

 similar experiments of various embryologists, we may conclude that in early 

 embryos the species differentials, or rather certain mechanisms of reaction 

 against such differentials, are not yet developed, and also that the bodyfluids 

 are not yet injurious to the strange transplant, but that not very much later 

 the harmful mechanisms develop in the embryo. However, as we have seen, 

 even during post-embryonal life the reactions against strange individuality 

 differentials are not as strong in very* young animals as in adults. In all these 

 cases it is necessary to distinguish between the presence of the organismal 

 differentials and of the reactions against the latter on the part of the strange 

 organism. The reactions may not yet be fully active at a time when the dif- 

 ferentials have already been completely formed. 



One of the characteristic features oi individuality differentials, and or- 

 ganismal differentials in general, is the lack of an injurious reaction of the 

 bodyfluids as well as of the cells of the host against cells or tissues which are 

 derived from the same organism, and which possess therefore the same in- 

 dividuality and the various other organismal differentials. This fact is ex- 

 pressed in our definition of individuality and organismal differentials. Simi- 

 larly, it is well known that, as a rule, it is not possible to produce antibodies 

 against autogenous normal cells, or against substances which represent a 

 normal constituent of the animal to be immunized, especially if it is accessible 

 to his bodyfluids. This applies also to the Forssman differentials, against which 

 antibodies can be produced only in those species which do not possess this 

 differential ; and the same holds good presumably in the case of the blood- 

 group differentials. It is a very interesting fact that if the blood cells of an 

 individual contain a certain agglutinogen, his blood serum lacks that particular 

 agglutinin which would interact with its own blood corpuscles and cause their 

 agglutination, and that thus the formation of agglutination thrombi and 

 emboli is avoided (Landsteiner). As we have discussed in an earlier chapter 

 Bernstein assumes that in every individual, to whatever blood group he may 

 belong, all the agglutinins are produced, including those which are able to 

 agglutinate his own corpuscles; but the latter kind of agglutinins are made 

 innocuous by union with the corresponding agglutinogens present in the 

 erythrocytes of the same organism, and only agglutinins which would act on 

 corpuscles belonging to other groups are left intact. Against this interpretation 

 may be cited the observation that injection of rabbits with human blood cor- 

 puscles of group A seems to cause the formation of anti-A immune agglutinins 

 only if the serum of these rabbits contains normally some anti-A antibodies, 

 which implies that the cells of this animal do not contain A receptors. But 

 if actually the A agglutinin was able to develop in a rabbit which possesses A 



