CHAPTER VI. 



THE NATURE OF OPSONINS 



The theories of Wright concerning opsonins have received 

 attention chiefly because of the apparent value of their quanti- 

 tative determination in health and disease and in the regulation of 

 dosage and interspacing of injections of bacterial- vaccines. Nu- 

 merous investigators, however, have attempted to determine their 

 importance in immunity, their structure, and the conditions 

 which influence their action. 



Wright has found opsonins, the substances which prepare bac- 

 teria for phagocytosis, present in the serum of normal, diseased 

 and vaccinated individuals. Neufeld and Rimpau, on the other 

 hand discovered substances which prepare bacteria for ingestion 

 by leucocytes, present in certain immune serum. Inasmuch as 

 both the opsonin of Wright and the bacteriotropin of Neufeld and 

 Rimpau perpare bacteria for phagocytosis, they are by many 

 considered as identical substances. Various investigators, while 

 admitting that these substances may be identical in some sera, 

 do not regard them as the same substances in all sera. Wright 

 has regarded opsonin as an important factor in immunity, but 

 has made no distinction between the opsonin present in normal 

 and immune sera. Numerous investigators, however, have dem- 

 onstrated and emphasized certain differences in the bacteriotropic 

 substances in normal and immune sera. 



SPECIFICITY. 



While Wright and Douglas did not discuss the question of 

 specificity of opsonins, still it is evident that they consider opso- 

 nins as specific. The opsonic index in disease, according to Wright, 

 shows certain deviations from the normal for certain microor- 

 ganisms, while for other organisms it deviates but little from the 

 opsonic index obtained with normal serum. On thisjDbservation 



