JOINT ACTION OF SEVERAL AMBOCEPTORS. 647 



ceptor the power of the horse serum to produce haemolysis in con- 

 junction with the ox serum is preserved. Moreover, when digested 

 with blood, such a serum suffers a smaller loss of this power than does 

 native serum. This also shows that the amboceptor bringing about 

 haemolysis is contained in ox serum. 



6. Bordet and Gay found that ox blood loaded with amboceptor, 

 (prepared), dissolves in a mixture of active horse serum and inactive 

 ox serum, but not in horse serum alone. This we were able to con- 

 firm. Their interpretation, however, according to which the ox 

 serum acts as a " colloid " in dissolving the ox blood previously pre- 

 pared with horse serum, and according to which this "colloid" is 

 bound by the prepared ox blood, this interpretation was shown to 

 be incorrect for the following reasons: 



7. Prepared ox blood absorbs the horse complement without 

 thereby being dissolved. Blood so treated, however, does not 

 dissolve on the addition of inactive ox serum, nor has it the power 

 to deprive the latter of its ability to bring about haemolysis. 



8. In fact, it has been found that even in the haemolysis of pre- 

 pared ox blood inactive ox serum and horse serum stand in direct 

 relations with each other. If both sera are digested prior to the 

 addition of the prepared ox blood, haemolysis will be markedly 

 hastened. 



9. Ox blood will also bind the horse complement if the blood is 

 first treated with a small quantity of amboceptor, although haemoly- 

 sis by horse serum and inactive ox serum requires a far greater 

 quantity of amboceptor. This shows that the immune serum 

 contains two different amboceptors. One of these, b, present in 

 high concentration, absorbs horse complement when ox serum is 

 absent, the other, a, present in weak concentration, binds horse 

 complement when ox serum is present. Only in the latter case 

 does haemolysis occur. 



10. Ox serum prevents the binding of horse complement by 

 weakly prepared (amboceptor b) ox blood, and yet does not give 

 rise to haemolysis in this case. 



11. Since, however, the ox serum acts on the horse serum and not 

 on the prepared blood, it follows that the ox serum binds a constituent 

 of the horse serum, which constituent has the power to make possible 

 and bring about the union of the horse complement and amboceptor 6. 



12. The combined action of the horse serum and inactive ox serum 

 in the haemolysis of prepared ox blood is thus explained by the 



