170 MODERN BIOLOGIC THERAPEUSIS 



tained accurately enough in single tests to be an 

 accurate guide for use in diagnosis or treat- 

 ment; and further, that the opsonic content is 

 not a safe guide for the measure of the total an- 

 tibodies in the blood. According to Wright 

 and Bullock, the opsonic index in normal indi- 

 viduals varies from 0.8 to 1.2. The deviation of 

 the index beyond these limits would indicate that 

 the patient was or had been infected with the 

 microorganism to which the variation in the 

 index existed. A low opsonic content, accord- 

 ing to Wright, denotes a lowered resistance and 

 a high opsonic content an increased resistance of 

 the individual to infection. The interest in the 

 subject of opsonins is largely due to the inves- 

 tigations and influence of Wright, who origi- 

 nated the idea of estimating the changes in the 

 opsonic power of the blood for the purpose of 

 guiding the use of vaccines in the treatment of 

 bacterial infections. 



The opsonic index has not been found of 

 much practical value for two reasons: (1) Be- 

 cause the technic of the test is not only time- 

 consuming but subject to error, so that consider- 

 able practice is necessary to obtain reliable re- 

 sults. (2) Variations which are great enough to 



