DIPHTHERIA BACILLUS. 347 



well understood, not for from two to four days. In 

 neutral bouillon the culture fluid frequently becomes 

 slightly acid and toxin production may be delayed for 

 from one to three weeks. The greatest accumulation 

 of toxin is on the fourth day, on the average, after the 

 rapid production of toxin has commenced. After that 

 time the number of living bacilli rapidly diminishes 

 in the culture, and the conditions for those remaining 

 alive are not suitable for the rapid production of toxin. 

 As the toxin is not stable, the deterioration taking place 

 in the toxin already produced is greater than the amount 

 of new toxin still forming. 



Bacilli, when repeatedly transplanted from bouillon 

 to bouillon, gradually come to grow on the surface 

 only. This characteristic seems to aid in the develop- 

 ment of toxin. 



The relations of toxin to antitoxin will be described 

 after the subject of antitoxin has been considered. 



Non-virulent Diphtheria Bacilli. Xerosis Bacilli. In 

 the very large number of tests for virulence of the 

 bacilli obtained from hundreds of cases of suspected 

 diphtheria which have been carried out during the 

 past six years in the laboratories of the Health De- 

 partment of New York City, in over 95 per cent, of 

 cases the bacilli derived from exudates or pseudomem- 

 branes and possessing the characteristics of the Loffler 

 bacilli have been found to be virulent, that is producers 

 of diphtheria toxin. But there are, however, in inflamed 

 throats as well as in healthy throats, either alone or 

 associated with the virulent bacilli, occasionally bacilli, 

 which though morphologically and in their behavior on 

 culture media identical with the Klebs-Loffler bacillus, 

 yet producers, at least in artificial culture media and 



