ORGANISMAL DIFFERENTIALS OF HYBRIDS 521 



were relatively slight and these investigators preferred therefore the use of 

 immune agglutinins, which they produced in rabbits by injection of the dif- 

 ferent types of red corpuscles. They tested the immune sera thus obtained as 

 to their action on the erythrocytes of horse, donkey and mule, either directly 

 or after previous absorption of the immune sera by the various types of 

 erythrocytes. All of these tests showed that the mule erythrocytes contained 

 agglutinogens of both horse and donkey. However, in the mule red corpuscles, 

 either not all of the donkey and horse agglutinogens were present, or they were 

 present in smaller amounts. As a rule, the immune serum prepared in rabbits 

 by injection of mule erythrocytes behaved more like anti-horse-corpuscle im- 

 mune serum than like anti-donkey immune serum, notwithstanding the fact 

 that the mule red corpuscles contain both kinds of agglutinogens. Horse as well 

 as mule erythrocytes could bind the immune agglutinins from immune serum 

 against mule corpuscles, including also the agglutinins which act on donkey 

 erythrocytes; but after a previous absorption of such sera by donkey red 

 corpuscles, a high agglutinin titer for horse and mule erythrocytes still 

 remained in the serum, while the donkey agglutinins had been removed. It 

 may therefore be concluded that as far as the production of immune sera can 

 be used as an indicator, the horse agglutinogens predominate in the red cor- 

 puscles of the mule. 



II. More recently Landsteiner studied, by means of immune hemolysins 

 and immune hemagglutinins, the relations of the blood of hybrids between 

 the domestic guinea pig (Cavia rufescens) and the wild Brazilian guinea pig 

 (Cavia porcellus) to the blood of the parent species. In this case Landsteiner 

 made use of homoio-immunization in order to eliminate the complication 

 which the strangeness between the donor of the blood and the animal to be 

 immunized would have introduced. Normally, no hemolysins or hemag- 

 glutinins are present in the blood serum of guinea pigs belonging to one 

 species or race for the erythrocytes of the other. But by injecting the blood 

 corpuscles of Cavia porcellus into Cavia rufescens it is possible to produce 

 immune hemolysins and immune agglutinins in the serum of the latter, which 

 act on the erythrocytes of Cavia porcellus, but not, as a rule, on the red cor- 

 puscles of Cavia rufescens. It was found that the red corpuscles of the hy- 

 brid behaved in an intermediate way; they contained characteristics of both 

 parents. This result corresponds to our findings in the analysis of hybrids 

 between different families in rats and in guinea pigs by means of transplanta- 

 tion. 



III. Irwin tested, by means of immune hemagglutinins, the relations be- 

 tween the domestic Ring dove ( Streptopelia risoria), the Asiatic Pearlneck 

 (Spilopelia chinensis), and the hybrids between these two genera. Rabbits 

 were immunized separately against the red corpuscles of the two parents and 

 of the hybrid and use was made of the absorption of the specific antibodies 

 by the various kinds of erythrocytes. It was found that the agglutinogens 

 of both parents were present in the erythrocytes of the hybrid, and that also 

 in the immune serum against the corpuscles of the hybrid, agglutinins against 

 the corpuscles of both parents could be demonstrated. However, the erythro- 



