PATHOGENIC BACTERIA. 343 



membrane, and that they not only appear in an apparent 

 healthy throat, especially in hospital nurses and in children 

 who have been associated with cases of diphtheria, but 

 also in those who have had no tracable contact with diph- 

 theria cases.* It has been found that bacilli sometimes 

 occur in the throat which have all the n morphological and cul- 

 tural properties of the diphtheria bacillus, but which are de- 

 void of virulence when tested upon animals. Such diphtheria 

 bacilli have frequently been called pseudodiphtheria bacilli. A 

 bacillus closely resembling the diphtheria bacillus, but without 

 virulence, has been found in xerosis of the conjunctiva. It is 

 called the xerosis bacillus. If not a transformed diphtheria 

 bacillus, it is at least closely related. The diphtheria bacillus 

 is subject to wide variations in morphology, so that, in dealing 

 with unknown cultures where the forms are not characteristic 

 and injection into animals is without result, it may be difficult 

 to decide whether or not the organisms are diphtheria bacilli. 

 Consequently another view with regard to pseudodiphtheria 

 bacilli has arisen. While recognizing that non-virulent diph- 

 theria bacilli occur, it is also claimed that a distinct pseudodiph- 

 theria bacillus exists, different from the diphtheria bacillus, 

 though resembling it. It is shorter, stains more evenly, shows 

 no polar granules by Neisser's method of staining, does not 

 produce acid in dextrose-bouillon, and is not pathogenic to 

 animals and does not produce diphtheria toxin. It is found 

 occasionally in the nose and throat and has no connection with 

 diphtheria, according to this view.f But there are some who 

 hold that there is no pseudodiphtheria bacillus, and that the 



*Sholiy. Journ. Inject. Dis. Vol. IV. 1907. pp. 337-346. 



f The different sides of this question will be found fully discussed by the 

 following: Wesbrook, Wilson and McDaniel. Transactions of the Association 

 American Physicians. 1900. Gorham. Journal Medical Research. Vol. VI. 

 1900. A. Williams. Ibid. Vol. VIII. 1902. Denny. Ibid. Vol. IX. 

 1903. Alice Hamilton. Journal of Infectious Diseases. Vol. I., No. 4. 1904. 

 Graham Smith. Journal of Hygiene. Vol. IV. 1904. 



