218 APPLIED IMMUNOLOGY 



active, additional injection of antigen will turn the 

 tide of battle against the individual and an otherwise 

 acute course be converted into a chronic or vital issue. 

 On the other hand, if the individual's defences are 

 great and his infection slight, an inoculation of bac- 

 terin may possibly increase his specific antibodies, 

 thereby enabling him to abort or at least shorten the 

 attack of his local infection. In the latter case, the 

 probability is that the patient if left to himself will 

 readily conquer his infection in due time. This dis- 

 crimination, in view of the danger involved, between 

 leaving Nature to herself and intervention by bacterin 

 therapy, can be made only by recourse to determina- 

 tions of the opsonic index. As a rule, these acutely 

 localized, particular^ if severe, and bacter^emic con- 

 ditions constitute realms for the wiser and more logical 

 practice of serum therapy or passive immunization. 

 Consensus of opinion generally supports the belief 

 that the bacteria best adapted to bacterin therapy or 

 active immunization are those containing the poison- 

 ous substances within themselves, the so-called " endo- 

 toxins," typified by the staphylococci and strepto- 

 cocci. Such bacteria do not liberate their endotoxins 

 until disintegration or death of their organism occurs. 

 On the other hand, diseases caused by the " exoteric " 

 or toxin-producing microorganisms, typified by diph- 



