56 BACTERIOLOGY FOR NURSES 



theria toxin for several weeks, or until the blood 

 contains the diphtheria antitoxin, which, when 

 injected in suitable quantities into the body of a 

 person who has been exposed to diphtheria, affords 

 a protection against the disease. The antitoxin of 

 diphtheria is also used as a curative measure. 



The accompanying table from Muir and Ritchie 

 shows the chief methods by which artificial immu- 

 nity may be produced, the principles underlying all 

 being the same : — 



Artificial Immunity 

 A. Active Immunity — i.e. produced in an animal by an injec- 

 tion, or by a series of injections, of non-lethal doses of an 

 organism or its toxins. 

 1. By injection of the living organisms. 



(a) Attenuated in various ways. Examples : — 



(1) By growing in the presence of oxygen, or in a 



current of air. 



(2) By passing through the tissues of one species of 



animal (becomes attenuated for another species). 



(3) By growing at abnormal temperatures, etc. 



(4) By growing in the presence of weak antiseptics, 



or by injecting the latter along with the organ- 

 ism, etc. 

 (6) In a virulent condition, in non-lethal doses. 



2. By injection of the dead organisms. 



3. By injection of filtered bacterial cultures, i.e. toxins; or of 



chemical substances derived from such filtrates. 

 These methods may also be combined in various ways. 



