ADAPTATION OF TISSUES AND THEIR PRODUCTS 471 



own red corpuscles and the serum of a species is likewise specifically adapted 

 to the red blood corpuscles of this species, although the adaptation between 

 the serum and cells within a certain species is not so perfect as that between 

 serum and cells within the same individual. Therefore autohemolysins do 

 not occur under ordinary conditions and, as a rule, cannot be produced 

 experimentally. Much more common, however, is the appearance of heter- 

 olysins. Examples of such a specific adaptation between blood serum and 

 erythrocytes may also be found in invertebrates; amoebocyte tissue which, 

 under certain conditions, results from the agglutination of the amoebocytes of 

 Limulus, remains better preserved in Limulus serum than in the sera of other 

 kinds of arthropods. 



Another example of the specific adaptation between the various constituent 

 parts of an individual is the following. Fresh serum or heparinized plasma 

 from normal dogs as a rule causes a local reaction in capillary permeability 

 when injected intradermally into other dogs, but this does not usually occur 

 when the injection takes place into the dog from which it had been obtained 

 (Freeman and Schecter). This is a further demonstration of an autogenous 

 equilibrium. On the other hand, the presence of a species equilibrium is 

 indicated, when, according to Togawa, injection of autogenous and homoioge- 

 nous serum causes an early increase in the amount of fibrinogen in the blood 

 of the injected animal, while heterogenous serum usually does not have this 

 effect. 



All these observations have one characteristic in common : they illustrate a 

 species or class or an autogenous equilibrium which latter we have analyzed 

 previously. The various constituent parts of an individual organism are 

 adapted to one another. Similarly the various components in the organiza- 

 tion of a species or class are adapted to one another. In a previous chapter 

 we have mentioned the fact that in more primitive organisms where it is not 

 possible to demonstrate the existence of individuality differentials, species or 

 class equilibria, indicating specific adaptations between the component parts 

 of these organisms, may be present. 



There exists a certain analogy between these specific adapations and the 

 specific adaptation between the red corpuscles and presumably other cells 

 belonging to a certain blood group and the serum of this group. In the latter 

 case, the specific adaptation manifests itself by the lack of an agglutinating 

 effect of the serum on the cells of the group to which both belong, although 

 such a serum agglutinates the cells of individuals belonging to other blood 

 groups which possess the necessary agglutinogen. But in this instance the 

 specific adaptation is not due to a real species differential but to a special 

 substance of a somewhat different nature. This relationship between serum 

 and erythrocytes serves to maintain the autogenous equilibrium. Bernstein, 

 however, interprets this phenomenon in a different manner; he assumes that 

 the antigen (agglutinogen) of a certain group, circulating in the blood unites 

 with the corresponding agglutinin and thus prevents it from becoming mani- 

 fest, while agglutinins which are able to combine with a strange agglutinogen, 

 not being bound by this antigen, remain active. However, if this explanation 



