THE OPSONIC THEORY. 



of saying that the infection is more virulent or 

 that his vital resistance has been reduced we 

 say the opsonic index is low. 



It is claimed by the discoverer that there Variation in 

 actually is a variation at different times in the S^the BlSd**"* 

 opsonic content of the blood. In other words 

 the blood of an individual will be stronger or 

 weaker in opsonic power, or the blood of the 

 same individual will be at different times 

 stronger or weaker in opsonic power as regards 

 each disease germ. 



That the leucocytes are powerless to fulfill 

 their function as phagocytes without the help 

 of opsonins is according to the advocates of 

 the theory entirely established. Without de- 

 scribing in detail the methods by which this 

 is proved it is sufficient to say that the ^°serum°"**'"*'^ 

 leucocytes isolated by appropriate methods and 

 mixed with living germs in a liquid saline 

 medium do not attack bacteria; but if blood 

 serum be added to the mixture of leucocytes 

 and bacteria the phagocytic activity begins at 

 once. This undoubtedly proves that the serum 

 contains some substance which enables the leu- 

 cocytes to attack and destroy the micro-organ- 

 isms. 



Wright has originated a very ingenious 



method of determining the opsonic power of 



the blood by comparing the opsonic potency of 



the blood of the individual under observation 



6i 



