238 LOUIS PASTEUR 



research institution, devoting itself to the conquest 

 of disease, was realized, and as he followed the 

 work of its able staff, he had reason to feel a pro- 

 found satisfaction in its achievements and promise. 

 Roux and Yersin had made a discovery of the 

 highest importance in regard to diphtheria. The 

 bacillus of this disease had been discovered by 

 Klebs in 1883, an d isolated and cultured later by 

 Loeffler. Roux found that the liquid filtered from 

 cultures of the diphtheria bacillus was highly poi- 

 sonous. A very small amount of this injected under 

 the skin of small animals caused death with many 

 of the symptoms of diphtheria, although, of course, 

 without the presence of the bacilli of diphtheria in 

 the body. Roux drew the conclusion that the 

 germs of diphtheria and presumably other germs 

 also produce their deadly effects through the pro- 

 duction of poisons or toxins. 



This discovery paved the way for another which 

 was made by Behring and Kitasato, the discovery 

 of antitoxins or substances produced by the body 

 which have the property of combining with and 

 neutralizing the toxins, and hence of relieving the 

 body from the poisonous effects which the latter 

 produce. The Pasteur Institute began to make the 

 antitoxin for diphtheria. By injecting gradually 



