IMMUNIZATION 



147 



blood, then the Maja serum disappears much more 

 rapidly than after the injection into a rabbit which 

 has not been treated with Maja serum before. The 

 effect of the previous injection of Maja serum is 

 therefore in this latter case just the opposite of that 

 observed if only some two or three hours have 

 elapsed between the first and the second injection. 

 The antidiphtheric serum consists of serum from 



Time in days — »- 



Fig. 35. 



an animal, generally a horse, which has been treated 

 with diphtheria toxin. If this horse-serum is injected 

 into the blood-vessels of another non-related animal, 

 such as a dog or a guinea-pig, precipitins against 

 horse-serum are secreted and found in the veins of 

 this animal. These precipitins may give precipitates 

 with the injected antidiphtheric horse-serum, which 

 precipitates show a great tendency to absorb sub- 

 stances from the blood. 



