7 6 IMMUNE SERA 



blood. " Possibly/' said they, " there exists a com- 

 plement of another animal which will fit the hypo- 

 thetical second substance of this dog serum." 

 This proved to be the case, the complement of 

 guinea-pig blood fulfilling the requirements. If 

 they added to the inactive normal dog serum about 

 2 c.c. normal guinea-pig serum the haemolytic prop- 

 erty was restored and the guinea-pig red cells 

 dissolved completely. According to Ehrlich, this can 

 only be explained by assuming that in guinea-pig 

 blood there exists a complement which happens to fit 

 the haptophore group of the second substance or 

 inter- body, of the normal dog serum. This com- 

 bination of guinea-pig blood, inactive normal dog 

 serum, and a reactivating normal guinea-pig serum 

 is well adapted to demonstrate the existence in 

 normal dog serum of an inter-body; for the guinea- 

 pig serum should be the best possible preservative 

 for the guinea-pig red cells. The haemolysis fol- 

 lowing the addition of this serum shows positively 

 the existence of a substance in the dog serum which 

 has acted with something in the guinea-pig serum. 1 



1 Of such combinations, i.e., combinations in which a com- 

 plement derived from the same animal from which the red cells 

 are derived fits to the inter-body of other species of animals, 

 causing the solution of red cells of the latter, Ehrlich and 

 Morgenroth found still other examples. For instance, guinea- 

 pig blood, inactive calf serum, guinea-pig serum; goat blood, 

 inactive rabbit blood, goat serum; sheep blood, inactive rabbit 

 blood, sheep serum; guinea-pig blood, inactive sheep serum, 

 guinea-pig serum. 



