VACCINE-THERAPY 63 



suffering from a bacterial infection and his opsonic index 

 to that infection stand at a certain point a further invasion 

 by another specific bacterium need not alter that index one 

 way or another. 



In estimating the opsonic power, we ascertain the follow- 

 ing valuable points : (1) what natural resources the animal 

 possesses — in other words, at what point his index stands ; 

 (2) during the progress of the disease we can note whether 

 that index rises or falls — in short, what efforts Nature her- 

 self is displaying in her endeavours to shake off the in- 

 vasion; (3) where we are adopting vaccine-therapy, the 

 index will assist us in forming an opinion regarding the 

 suitability of the dose, and to what degree the patient 

 responds to our vaccine stimulus. 



Of course, as we shall see later, clinical observations on 

 these three points also are of great assistance to us in 

 forming our conclusions upon the various phenomena and 

 immunizing responses made manifest during the progress 

 of a specific disease. Although in practice the taking 

 of the opsonic power is not essential to success, it gives 

 us a very valuable and very delicate guide to follow, and 

 well repays the practitioner who will take the extra trouble 

 to work it out. 



The Usual Method adopted in estimating the Opsonic 

 Power of the Blood. 



1. Take a Wright's blood-capsule, and, after sterilizing 

 the skin over one of the facial veins of an animal belonging 

 to the same species as the patient, puncture the vessel with 

 a small lancet, and collect the blood in the capsule. In 

 like manner collect the blood from the patient at or nearly 

 at the same time, since opsonin after a length of time 

 becomes inert. 



2. Take the bacterial growth we desire to test, and not 

 more than twenty-four hours old. Add 1 or 2 c.c. of normal 

 saline solution to the culture-tube ; shake gently to wash off 

 the colonies. The resultant emulsion should be pipetted off 



