376 INFECTION AND IMMUNITY. 



subsequent to the introduction of the organisms. 

 Clinically,, we are familiar with them as failures. 

 It is particularly in relation to the streptococ- 

 cus that the so-called polyvalent serums have been 

 prepared. Cultures of streptococcus obtained 

 from numerous sources are used in the immuniza- 

 tion with the expectation that the serum will be 

 effective against various strains of streptococci. 

 The principle may be an important one in the 

 preparation of other antibacterial and bactericidal 

 serums. 



(C) VACCINATION. 



vaccination We are most familiar with the terms vaccine 

 \u and .vaccination as applied to protective inocula- 

 tion against smallpox. They are used, however, 

 with equal propriety in all instances in which the 

 attenuated or killed virus of a disease is inoculated 

 f5r~Ehe purpose of establishing resistance to an 

 infection.) The process set in motion by vaccina- 

 tion is one of active immunization in which the 

 cells are induced to form specific antibodies over a 

 long period; hence, the resistance is more pro- 

 tracted than that established by passive immuni- 

 zation. 



Certain experimental work, as previously stated, 

 indicates that the acquired resistance persists after 

 the formation of antibodies has ceased, even after 

 the quantity of the latter has sunk to the normal. 

 This condition has been explained by assuming 

 that, as a consequence of vaccination, the cells of 

 the body have been "trained" to produce the cor- 

 responding receptors; hence, when the micro-or- 

 ganisms gain entrance at a subsequent time new 

 antibodies are formed so rapidly and in such abun- 

 dance that the incipient infection is overcome. 



