128 IMMUNE SERA 



Opsonins Distinct Antibodies. It was natural to 

 question whether these " opsonins " were really dis- 

 tinct from other antibodies, or whether they were 

 perhaps identical with the immune body (or sub- 

 stance sensibilatrice). In a series of papers on this 

 subject Hektoen * shows that the former is the case, 

 opsonins are distinct substances. This is not only 

 indicated by the results of absorption tests, but by 

 the fact that, by immunization, a serum can in cer- 

 tain cases be obtained which is opsonic but not lytic, 

 or in other cases one which is lytic but not opsonic. 

 Similar experiments have differentiated opsonins 

 from agglutinins. 



Structure of Opsonins. Opsonins, like agglu- 

 tinins and precipitins, appear to possess two groups, 

 opsoniferous and haptophore. On heating an op- 

 sonic serum the former group is destroyed but the 

 haptophore group remains intact, as can be seen from 

 suitable combining experiments. There is still con- 

 siderable difference of opinion as to the degree of 

 heat necessary to inactivate the opsonins. Once the 

 opsoniferous group has been destroyed it is impos- 

 sible to restore the opsonic action by the addition 

 of a complementing substance. Hence the opsonins 

 are to be regarded as receptors of the second order 

 and similar in structure to the agglutinins and 

 precipitins. 



The Opsonic Index. In the study of these opso- 



1 Hektoen, L., Journal Infect. Diseases, 1905 and 1906. 



