208 OPSONIC INDEX 



for a certain microorganism indicates that this organism is probably the 

 etiologic factor. This possibility is strengthened if the opsonic index 

 for this microorganism is increased by careful manipulation or exercise 

 of the diseased part, when auto-inoculation occurs, with consequent 

 increase of opsonin. 



4. In prognosis the opsonic index may have some value in deciding 

 whether an infection has been entirely overcome or is still active. An 

 attempt is made to induce auto-inoculation, as by gentle massage of a 

 knee-joint or a hip; active exercise; deep breathing, etc., and the in- 

 dex is made before, and at frequent intervals after, such attempts. If 

 the index remains unchanged within the normal limits, the assumption 

 is that the infection has been overcome; if, on the other hand, an in- 

 crease in opsonin occurs, this indicates that an active focus remains. 



5. Most value was placed by Wright upon the opsonic index as a 

 guide to the size and frequency of doses of bacterial vaccines in the treatment 

 of disease. A large number of careful determinations showed that an 

 injection of vaccine is followed by a decrease of the opsonins (negative 

 phase), which is of variable degree and duration, according to the amount 

 injected (Fig. 55). This is followed by an increase (positive phase), 

 and coincidentally there is a corresponding improvement in the patient's 

 condition. This subject is discussed more fully in the chapter on Active 

 Immunization. 



The purpose of proper vaccination, therefore, is so to gage and 

 time the different doses that a pronounced or prolonged negative phase 

 is prevented, as far as possible, and a high positive phase secured and 

 maintained. It is obvious that the technic of opsonic measurement con- 

 sumes much time, and that the immunisator cannot mark the index at 

 the time a dose of vaccine is given. However, the determination of the 

 opsonic index at proper intervals after the first dose of vaccine may give 

 valuable information as regards the reaction of the patient, and serve 

 as a guide to the size and frequency of subsequent doses. 



As a routine measure, the opsonic index has fallen into disuse, vac- 

 cine therapy being largely guided by the clinical evidences of reaction 

 and the condition of the patient. That it has distinct value, particularly 

 in scientific investigation, is generally admitted, and it is well to re- 

 member that in the early years following Wright's investigations the 

 practice of vaccine therapy was limited to those skilled in determining 

 the index, preparing the vaccine, and carefully guiding and guarding 

 its administration. It is to be regretted that the wholesale and indis- 



