ORGAN (TISSUE) DIFFERENTIALS 537 



either in the extracts or suspensions of certain organs or in chemically 

 defined substances obtained from and characteristic of such organs. We 

 shall consider only certain of those substances concerning which there are 

 on hand data sufficient for this analysis. 



1. It is known that a comparison of the blood sera of various groups of 

 animals, when tested by means of the precipitin reaction, indicates the degree 

 of relationship of these animals within a somewhat limited range of specificity. 

 We have furthermore seen that different serum proteins show a definite 

 substance-specificity when tested with precipitin containing immune sera; 

 but a specific reaction takes place in the latter case only if the antigen and 

 the corresponding substance with which it is to be compared belong to the 

 same or to nearly related species (Hektoen and Welker). Thus, immune 

 serum directed against the serum globulin prepared from human serum 

 reacts only with the globulin prepared from human or from monkey blood. 

 Immune serum against fibrinogen prepared from mammalian blood reacts 

 strongly with mammalian but only weakly with chicken fibrinogen, while con- 

 versely, anti-chicken fibrinogen serum reacts strongly with chicken and but 

 little with mammalian fibrinogen. By means of absorption of the immune 

 serum by the principal antigen, all the antibodies can be removed from the 

 immune serum, but absorption with the corresponding antigens from other 

 species removes only the special antibodies which are adjusted to the latter 

 kinds of antigen, while the principal antibody, namely that which is directed 

 against the fibrinogen of the species which was used for immunization, 

 remains in the serum. Much finer are the differences between the albumins 

 from the egg of different species. Here the investigations of Dale and Hartley, 

 who used the anaphylactic method, at first seemed to indicate an identity 

 between the crystallized albumins of fowl and duck eggs, but by the use of 

 more refined methods Dale succeeded in distinguishing between these two 

 substances also immunologically. Such a result suggests that in other cases 

 as well, when apparently no immunological differences exist between two 

 corresponding proteins from two species, such differences after all may exist. 



These observations show that we may have to deal in these instances not 

 only with organ differentials, but also with organismal differentials. Like- 

 wise with casein, it seems possible that a combination between a substance- 

 (organ) and an organismal-specificity exists, although by means of immune 

 reactions apparently no differences between the antigenic effects of different 

 mammalian caseins can be established. 



2. Hemoglobin possesses a distinct substance-specificity, corresponding to 

 a tissue- or organ-specificity ; the immune serum against this substance con- 

 tains specific precipitins. However, an immune serum against hemoglobin 

 of a given species reacts not only with the hemoglobin from this species, 

 but also with the hemoglobin from nearly related species, but not with 

 that derived from a distant species. Thus immune serum against cattle 

 hemoglobin may react also with a solution of sheep hemoglobin, but not 

 with a solution of hemoglobin from farther distant species; exceptionally, 

 this immune serum reacts with human hemoglobin, but only if it is used in 



