Passive Acquired Immunity 97 



animal may need no additional immune body, or, receiving 

 it, may be unable to use it because of deficient complement, 

 and under such circumstances may even be injured by it, 

 through the formation of anti-immune body by which com- 

 plementary substance subsequently formed may be rendered 

 inactive because of the neutralized immune body present in 

 its blood. It is, therefore, doubtful whether an immune 

 serum will be useful in assisting the animal i. e., producing 

 passive immunity in these cases. 



On the other hand, the administration of a serum contain- 

 ing complementary substance is made difficult because of 

 our inability experimentally to increase the complements 

 normal to the blood. The administration of normal fresh 

 serum sometimes supplies enough complement to enable the 

 dissolution of bacteria to take place, but the quantity is 

 usually so small that no appreciable benefit obtains. 



Passive immunity may also be brought about in a few 

 cases by the injection into the intoxicated animal of sub- 

 stances, other than immunity products, that have a specific 

 affinity for the poison. Thus Wassermann and Takaki* 

 found that when the crushed spinal cord of a rabbit was 

 mixed in -vitro with tetanus toxin, the poison was quickly 

 absorbed by the nerve-cells, so that the mixture became 

 inert and could be injected into animals without harm. 

 Wassermann also found that the same effects could be pro- 

 duced in the bodies of animals, and that when the crushed 

 spinal cord was injected into an animal twenty-four hours, 

 or a few hours previously, or a few hours after a fatal dose of 

 tetanus toxin, enough of the combining elements remained 

 in the blood to fix the toxin before it anchored itself to the 

 central nervous system of the intoxicated animal. Myersf 

 found that the ground-up tissue of the adrenal bodies was 

 able to fix and thus annul the poisonous effects of cobra 

 venom in vitro. 



In all these cases the neutralizing effects are either accom- 

 plished or initiated by factors prepared experimentally, and 

 forced upon the animal in whose body their activities are 

 manifested. 



* " Berliner klin. Wochenschrift," Jan. 3, 1898. 

 t" Lancet," July 2, 1898. 



