THE BACILLUS AND THE BACTERIOLOGY OF DIPHTHERIA 195 



the culture fluid frequently becomes slightly acid and toxin production 

 may be delayed for from one to three weeks. The greatest accumula- 

 tion of toxin is on the fourth day, on the average, after the rapid pro- 

 duction 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 development of toxin. 



The relations of toxin to antitoxin will be considered later in this 

 chapter. 



Diphtheria-like Bacilli Not Producing Diphtheria Toxin. In the tests 

 of the bacilli obtained from hundreds of cases of suspected diphtheria 

 which have been carried out during the past ten years in the labora- 

 tories of the Health Department of New York City, in over 95 per 

 cent, of cases the bacilli derived from exudates or pseudomembranes 

 and possessing the characteristics of the Loeffler 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-Loeffler bacillus, are yet producers, 

 at least in artificial culture media and the usual test animals, of no diph- 

 theria toxin. Between bacilli which produce a great deal of toxin and 

 those which produce none we find a few of minor grades of virulence. 

 We believe, therefore, in accordance with Roux and Yersin these non- 

 virulent bacilli should be considered as possibly attenuated varieties 

 of the diphtheria bacillus which have lost their power to produce diph- 

 theria toxin. These observers, and others following them, have shown 

 that the virulent bacilli can be artificially attenuated; but the reverse has 

 not been proven that bacilli which produce no specific toxin have later 

 been found to develop it. In our experience some cultures hold their viru- 

 lence even when grown at 41 C. for a number of months, while others 

 lose it more quickly. Diphtheria-like bacilli are also found which 

 resemble diphtheria bacilli very closely except in toxin production, 

 but differ in one or more particulars. Both these and the character- 

 istic non-virulent bacilli are found occasionally upon all the mucous 

 membranes! both when inflamed and when apparently normal. From 

 varieties of this sort having been found in a number of cases of the 

 condition known as xerosis conjunctive, these bacilli are often called 

 xerosis bacilli. Under this name different observers have placed bacilli 

 identical with the diphtheria bacilli and others differing quite mark- 

 edly from them. 



Bacilli Virulent to Guinea-pigs in Spite of Producing no Diphtheria 

 Toxin. These bacilli are obtained fairly frequently from normal or 

 slightly inflamed throats and may be only slightly pathogenic in 



