452 DIPHTHERIA, SCARLET FEVER, AND TETANUS 



mixture into healthy guinea pigs, they died. From these experi- 

 ments, he concluded that guinea pigs which had contracted and 

 recovered from diphtheria had something in the serum that safe- 

 guarded them from subsequent attacks of the disease. He called 

 this protective material antitoxin. His experiments showed that 

 the guinea pig's body made protective antitoxins to combat the 

 toxins of bacilli. These antitoxins remained in the blood of 

 animals that recovered from diphtheria. 



He then decided to prepare an immune serum which would 

 protect babies. He injected small amounts of diphtheria toxins 

 into sheep and continued to give them doses of increasing strength. 

 Ultimately, the sheep were immune to the most powerful diph- 

 theria bacilli. Then he injected serum from the immune sheep 

 into guinea pigs and later he inoculated diphtheria bacilli into 

 these pigs. They were not affected by the bacilli. Evidently, 

 the antitoxins made by the sheep's body were effective in pro- 

 tecting the guinea pigs against diphtheria bacilli. One serious 

 difficulty was that this immunity did not last. In 1891, Von 

 Behring discussed the use of serum on babies, and in 1893 it 

 was first used in the Children's Hospital in Berlin with some 

 degree of success. 



The discovery of active immunity. The fact that sheep, goats, 

 and horses used in the production of antitoxin seemed to develop 

 a permanent immunity to the diphtheria toxin gave the basis for 

 the next step in this work. Persons who had once been sick with 

 diphtheria seemed to be free from further attacks. This gave 

 support to the idea that the presence of toxins stimulates the 

 human body to produce its own antitoxins. The action of the 

 body in producing its own protective material is known as active 

 immunization, and the resulting condition is active immunity. 



Investigators mixed antitoxin with toxin and found that the 

 toxin was rendered harmless. Von Behring was the first to 

 attempt to give a permanent immunity to children by means of 



