PRODUCTION OF ARTIFICIAL IMMUNITY. 427 



protect other animals from lethal doses of toxine. To such 

 a serum the term antitoxic was applied, though the serum 

 protects against the living organisms also. In other diseases 

 a similar method was afterwards employed by injecting the 

 living organisms in gradually-increasing doses, the serum of 

 the animal thus immunised being effective in protecting 

 another animal from infection with the organism. Such a 

 serum is, in the first instance, antimicrobic. The re- 

 lations of the antitoxic to the antimicrobic property will 

 be discussed later, but for facility of description it is advis- 

 able to consider them separately. 



In the accompanying table a sketch of the chief methods 

 by which an immunity may be artificially produced is given. 

 It has been arranged for purposes of convenience and to 

 aid subsequent description, and it is not to be inferred that 

 all the different methods imply essentially different principles. 

 There is still some doubt as regards the relation of A 2, for 

 example, to A i and A 3. 



ARTIFICIAL IMMUNITY. 



A. Active Immunity i.e., produced in an animal by an 

 injection, or by a series of injections, of non-lethal 

 doses of an organism or its toxines. 



i . 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 organism, etc. 



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



