CHAPTER V. 



OPSONIC INDEX IN HEALTH AND 



DISEASE. 



The active participation and function of the white blood cells 

 in the protection of the body against infection was first carefully 

 studied by Metchnikoff. He regarded the leucocytes as cells 

 whose object is to remove from the body and its tissues bacteria 

 and foreign material. On this he based his theory of immunity. 

 It is not strange that Leishman, Wright, and others should have 

 suspected differences in phagocytosis in health and disease. In 

 1902 Leishman, and especially Wright, emphasized the difference 

 in phagocytic ratio observed in individuals with infections run- 

 ning favorable or unfavorable courses. While trying to find a 

 method by which to control the administration of vaccine, Wright 

 discovered opsonins. With the discovery of opsonin and the 

 development of a method for the determination of the same, it 

 was evident that the opsonic index in health and disease should 

 be investigated. Wright found that in individuals with localized 

 or chronic infections there is usually a decrease in the opsonin 

 content of the blood. This decreased opsonin content as deter- 

 mined by the opsonic index, according to Wright's theories, is 

 due to the fact that in local infections but little of the bacterial 

 substance is absorbed, and so gives rise to but a small amount of 

 active immunity. When this is the case the local infection be- 

 comes chronic. 



By the method of the determination of the opsonic index, 

 Wright has demonstrated that following the injection of vaccines 

 made from the cultures of infecting organisms, there is first a 

 drop in the opsonic index and later a rise of the same. The drop 

 in the index he calls the "negative" phase and the rise the "posi- 

 tive" phase. The observation of negative and positive phases 

 was made by Ehrlich in 1892, who found that following in- 



