TWENTY-FIVE YEARS OF BACTERIOLOGY 123 



was to extend rather than to retard and confound knowl- 

 edge. We are moving now in more peaceful times, the 

 heat of the earlier conflicts having largely subsided, and 

 it may be stated that neither the one nor the other doctrine 

 finally triumphed, but that the humors or fluids of the 

 body on the one hand and the cells on the other have come 

 to be recognized as the active participating factors in the 

 immunity process, the one complementing the other. 

 Where the phenomenon is one purely of the neutralization 

 of a poison or toxin, the fluid portion of the blood suffices ; 

 where also the process is relatively the simple one of act- 

 ing on and dissolving a bacterial cell, there also the fluid 

 may suffice, although an essential element in the process 

 may have been supplied by the white blood cells at the 

 moment of their withdrawal from the body. But where 

 the bacteria are not readily disintegrated and dissolved, 

 there the phagocytes of the blood and tissues come into 

 play and, through their power of engulfing these particles, 

 operate as one of the body's main defenses against in- 

 fection. 



The unraveling of the intricacies of the immune state, 

 following upon the work of Behring, has brought about 

 a sudden and unprecedented enlargement of the scope of 

 bacteriology, as well as supplied a wealth of new facts 

 of which many have permanently enriched practical medi- 

 cine and opened new territory to profitable exploration. 

 It may suffice at this point merely to mention certain of 

 the devices for diagnosis and means of preventing or of 

 treating disease, which are the immediate heritage of 

 studies in the field of immunity, of which many have 

 come not as direct fruits, but as invaluable by-products of 

 the search. In this manner have been secured the Widal 

 test for typhoid fever, the Wassermann and allied reac- 

 tions, the hypersensitive or Schick test for diphtheria 

 susceptibility, the hypersensitive reaction as now applied 

 to the detecting of the offending agency in hay fever and 

 allied states, the refinements of bacterial vaccination in 



