VACCINE OR OPSOlftC THERAPY 101 



tain substances termed opsonins, which prepare the 

 bacteria for destruction by the phagocytes, that is, so 

 act upon the bacteria as to render them susceptible 

 to the action of the phagocytes. Wright discovered that 

 the amount of these opsonins in the blood which, by 

 the way, differ for different bacteria, could be increased 

 for any particular germ by injection into the body of 

 dead cultures of that germ. These dead cultures are 

 called bacterial vaccines. They should not be confused 

 with the vaccines for small-pox and anthrax, which 

 depend upon a different principle, which will be consid- 

 ered later. 



The Opsonic Index. The amount of opsonins for 

 a certain germ present in the blood of an individual may 

 be determined in the following manner: 



Equal volumes of blood-serum and of leukocytes from 

 the blood of the individual, which have been Washed with 

 normal salt solution, and of emulsion of a culture of 

 the germ in question, are mixed and placed in an incu- 

 bator for fifteen minutes. We have then phagocytes, 

 germs, and blood-serum containing the opsonins, more 

 or less of which the individual may be possessed. Cover- 

 slips of the mixture are then made, stained, and examined 

 under the microscope, when the number of bacteria 

 contained in each leukocyte may be seen and counted. 

 The number of bacteria in 50 or more leukocytes are 

 counted and averaged. 



The opsonic index is simply a method of expressing 



