38 APPLIED IMMUNOLOGY 



Antitetanic and other antitoxic sera are produced 

 and tested in a similar manner, the horse being the ani- 

 mal usually immunized for their production. 



Preparation of Antibacterial Sera 



The bacteria belonging to this group do not act by 

 means of extracellular toxins. Their deleterious ef- 

 fects depend upon toxins set free from the bacterial 

 protoplasm when the organisms undergo disintegra- 

 tion (endotoxins). These toxins cannot be separated 

 from the bacteria themselves in vitro, except to a very 

 slight extent. At any rate it is doubtful if the sub- 

 stances which call forth the production of antibodies 

 can be thus separated. Antibacterial sera are there- 

 fore produced by injecting the bacteria themselves 

 into the body of the animal that is to be actively im- 

 munized. These are injected, usually at first inac- 

 tivated, but also at times in an attenuated or even in 

 their living state (Fig. 2), in gradually increasing 

 doses until an antibacterial serum of suitable strength 

 is obtained, when the animal is bled, and the serum 

 preserved in ampoules containing convenient doses for 

 therapeutic injection. The antibodies contained in 

 antibacterial sera are not of the comparatively simple 

 nature of those found in antitoxic sera, but belong to 

 the second and third orders of Ehrlich. The action of 

 antibacterial sera depends upon several factors, in- 



