IMMUNITY 63 



in the blood by subcutaneously injecting into the patient 

 a carefully measured quantity of vaccine (sterile bac- 

 teria). The increased phagocytosis which results is not 

 due to any direct stimulation of the leucocytes. The 

 newly formed opsonins are in the blood-serum and act in 

 some unknown way on the bacteria, so changing them 

 that the white blood corpuscles, or scavengers of the body, 

 greedily eat them up. Careful experiments have shown 

 that leucocytes washed free of serum and brought into 

 contact with an emulsion of bacteria show no phagocytic 

 action, while if they are brought into contact with the 

 same organisms which have been previously bathed in 

 blood-serum and the serum then carefully washed off, the 

 microbes are rapidly engulfed by the leucocytes. 



"A personal vaccine is prepared, when possible, by iso- 

 lating the organism from the infected individual, but as 

 the preparation of the vaccine requires several days after 

 the organism has been isolated, the first dose is usually 

 given from the " stock bottle." Stock bottles of vaccine 

 made from pure cultures of various kinds of bacteria are 

 kept in an opsonic laboratory, each bottle of course con- 

 taining only one kind of bacteria, e.g. staphylococcus. 

 Since it requires nearly three months to cultivate the 

 tubercle bacillus on artificial media, it is plainly evident 

 that it is impracticable to treat tuberculous patients with 

 personal vaccines. 



" The normal opsonic index is 1.0, that is, there is in the 

 blood of normal individuals practically an equal measure 

 of opsonins. The object of opsonic therapy is to raise 

 and maintain the opsonic index as high as possible above 



