176 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



satisfactory manner; if animals of the latter type were used, disharmony 

 appeared earlier. Inasmuch as the conclusion is justified that the local re- 

 actions affecting transplanted skin are due to the action of strange individu- 

 ality differentials, it seems also justifiable to conclude that, essentially, dif- 

 ferences in individuality differentials are the cause of the disharmony which 

 develops sooner or later in parabionts. Schoene, Majeda, and others, found 

 furthermore that instead of improving the outcome of homoiogenous trans- 

 plantation of skin, parabiosis, on the contrary, seemed to make the results 

 more unfavorable, and similar observations were made also in autotrans- 

 plantation. It is possible that the intensified injury, inflicted upon homoi- 

 ogenous transplants as a result of parabiosis, is caused by an increase in the 

 immune reactions against strange individuality differentials taking place 

 under homoiogenous conditions. As to the injurious effect on autogenous 

 grafts, we must consider the fact that a real autogenous transplantation in 

 parabiotic animals is not possible, inasmuch as homoiogenous individuality 

 differentials, even if much diluted, are continuously given off by the partner 

 and must, to some extent, affect the condition of the autotransplant. 



We may then conclude that in all probability strange individuality differen- 

 tials are responsible for the injurious general as well as local reactions affect- 

 ing partners in parabiosis, as for instance, for the damage inflicted on 

 transplanted pieces of skin or of other organs, but that in addition to these 

 primary direct actions of the strange individuality differentials, also immune 

 reactions against these antigens may be active. 



We have referred already to the analogy which exists between the state of 

 pregnancy and that of parabiosis. However, pregnancy differs from true 

 parabiosis in three respects : ( 1 ) In pregnancy, we have not to deal with the 

 union of two formerly independent partners, able to sustain themselves in a 

 free state, but with the development of an embryo and fetus inside the 

 mother's organism; (2) the blood vessel connections between fetus and 

 mother, by way of the placenta, are much more extensive than those exist- 

 ing between true parabiotic partners, and (3) the embryo and fetus receive 

 essential foodstuffs from the mother. During pregnancy there is no indication 

 that strange individuality differentials injure fetus or mother. Perhaps an 

 enlargement of the lymphatic organs which may appear in the fetus might 

 point to a late effect of strange individuality differentials, but this inter- 

 pretation appears uncertain at present. On the other hand, it has been shown 

 that in some rare cases antibodies may develop in the mother against blood 

 group differentials present in the fetus, a point which has already been dis- 

 cussed. It is probable that during embryonic and fetal development an adap- 

 tation takes place against strange individuality differentials in both mother 

 and fetus. 



Also, parasitism may be considered as a condition resembling parabiosis. 

 But this condition differs from true parabiosis in the very great inequality 

 distinguishing host and parasite. The parasite lives at the expense of the host 

 and is adapted in a peculiar manner to the host and to one or more of its 

 organs. A further discussion of this relationship will be taken up in a later 

 chapter. 



