260 LECTURES ON IMMUNITY 



criticism. We only remark that the compound is very 

 easily dissociated, so that it was only with the help of 

 quantitative measurements that a proof of its presence 

 could be given (cf. p. 224). As this compound occurs in 

 the erythrocytes, it would seem very improbable that it 

 should not exist also outside of the erythrocytes, although 

 dissociated to a high degree. 



As we have seen above, Ehrlich and Sachs made experi- 

 ments with erythrocytes from guinea-pigs, normal bovine 

 serum heated to 56 C. (which they regarded as immune- 

 body), and alexin from horse blood. They found that the 

 haemolytic agent from the bovine serum was not absorbed 

 by the erythrocytes, for it did not lose its activity after 

 having been shaken with such erythrocytes. Hence they 

 concluded that not the immune-body, but its compound 

 with alexin, is absorbed by the erythrocytes. This con- 

 clusion is not corroborated by the investigation of Bordet 

 and Gay, for they found that if they used alexin from 

 guinea-pigs instead of alexin from horses, haemolysis oc- 

 curred, but not after the immune-body had been separated 

 from the bovine serum by treatment with erythrocytes 

 from guinea-pigs. There must therefore be another ex- 

 planation of the experiments of Ehrlich and Sachs. After 

 a thorough investigation, Bordet and Gay conclude that 

 the normal horse-serum, used by Ehrlich and Sachs, 

 furnishes not only the alexin, but also the immune- 

 body to the erythrocytes. The compound haemolysin 

 of these two substances is too weak to cause a percep- 

 tible haemolysis, but it is strengthened by the presence 

 of some substance contained in the bovine serum, which 

 they call "colloide de boeuf." This colloid is indeed 



