THE OPSONIC INDEX 237 



the " ebb " is less conspicuous and the " positive 

 phase " becomes sustained. At this time the patient 

 is said to be on the " high tide of immunity " and 

 further inoculations are contra-indicated. This is ob- 

 served in connection with prophylactic inoculations 

 and where recovery is apparent. Wright's original 

 rule was to take the opsonic index daily and be guided 

 exclusively by its indications ; at present, although the 

 value of the index is not belittled, the clinical course 

 of the case is utilized as an important guide in treat- 

 ment. Inoculations are not repeated until positive 

 phase symptoms are no longer apparent, or in doubt- 

 ful cases determination of the index demonstrates a 

 fall in opsonins. So long as there occurs any benefi- 

 cial response whatever from a bacterial inoculation, 

 its size, whether the " minimum effective " or the 

 " medium or average," is not increased. 



The " ideal curve " consists of a " negative phase '' 

 of twelve or twenty-four hours, followed by a " posi- 

 tive phase " lasting from three to fourteen days. This 

 curve depends upon two factors, (1) the size of the 

 dose and (2) the vital resistance of the patient. A 

 small dose may have to be repeated frequently, possi- 

 bly every day, owing to the short duration of the 

 " positive phase," whereas a large dose may necessi- 

 tate the suspension of any further inoculations on ac- 



