174 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



surviving, dominating animal is usually not quite so well as it would have 

 been in the free state. In this disharmonious phase the tone of the blood 

 vessels is gradually lowered, especially in the weaker partner and towards 

 the end of its life, consequently the stronger partner pumps a considerable 

 part of its blood into the weaker one, which thus becomes hyperemic and 

 polycythemic, while the dominating partner is made anemic. The diminished 

 erythrocyte-destroying function of the spleen of the weaker animal has also 

 been held responsible for the developing polycythemia. In this animal there 

 are, in addition, atrophic changes in the inner organs and at last a fibrosis 

 of the bone marrow may occur ; in the stronger partner there occurs, on the 

 contrary, a stimulation of the various lymphatic organs and of the bone 

 marrow, with corresponding changes in the circulating cellular elements 

 originating in the bone marrow. Nodules consisting of reticular-endothelial 

 tissue may develop and accumulations of plasma cells may appear in the 

 connective tissue. As a rule, the weaker hyperemic partner, whose heart is 

 overloaded with blood, dies first, but occasionally the dominating though 

 anemic partner may succumb earlier. 



As to the cause of the disharmony which may develop, as early as in the 

 second or third week after the union has been established, but much later 

 in other cases, various suggestions have been made. Which of the two 

 partners will be the less resistant one and will be ultimately suppressed 

 seems usually to be determined by accidental factors, such as the presence 

 of some inferiority, as for instance, lack of a kidney, at the time when 

 parabiosis was established. The fact that disharmony develops at all has 

 been attributed by some investigators to a state of undernourishment, on 

 the assumption that the stronger partner deprives the weaker one of food- 

 stuffs ; however, the weaker partner often consumes a large amount of food 

 and, also, the stronger partner may lose somewhat in weight. According to 

 Hermannsdorfer, disharmony arises from the passing of intermediary 

 metabolic products from one animal to the other. The increased toxicity of 

 the urine in parabiotic animals, as indicated by the production of convul- 

 sions in other animals injected with such urine, has been considered as due 

 to these substances. However, it is not probable that such metabolic products, 

 which are present and are about the same in all normal individuals of the 

 same species, are the essential cause of the disharmonious state. 



Another view as to the underlying factor in this condition is held by a 

 number of authors, who believe that a state of chronic anaphylaxis exists, 

 due to the constitutional biochemical differences between the two partners, 

 such differences arising from inherited differences in various organs. The 

 dilatation of the vessels which is observed in the weaker partner is often 

 cited as an important argument in favor of this view ; but, this condition of 

 the vascular system may be the result of general weakness rather than of 

 specific anaphylaxis. Furthermore, if the two partners during the phase of 

 disharmony are separated, a recovery of both may take place, and if subse- 

 quently, parabiosis is re-established, no sign of hypersensitiveness becomes 

 noticeable. Moreover, the production of the well-known immune substances, 

 such as hemolysins, agglutinins, or precipitins, can not usually be demon- 



