Upon the Pseudo- Diphtheria, etc. 51 



distinct, namely : those which grow as a distinct layer upon 

 these media, forming a rather thick, creamy-white surface- 

 growth, and the group comprising those which grow only, 

 or usually at least, as small, pearly-white, isolated colonies 

 on these media. The former group comprises the organ- 

 ism which is usually designated as the pseudo-diphtheria 

 bacillus, or Hofmann bacillus. The latter group comprises 

 what is usually known as the xerosis bacillus. Morpholog- 

 ically, these two groups of organisms resemble each other 

 very closely, and they also resemble the L,6ffler bacillus 

 quite closely, so much so that their occurrence in cul- 

 tures made for the diagnosis of diphtheria is sure to lead 

 to errors in diagnosis unless the precaution is taken to 

 apply Neisser's differential stain. Our experience has been, 

 however, that where this differential staining method has 

 been systematically employed a safe differential diagnosis 

 can be made, from the fact that neither of these groups 

 of organisms shows the polar granules of Neisser when 

 grown under the prescribed conditions. 



There has been for some time considerable controversy 

 between bacteriologists with regard to the identity of these 

 micro-organisms. Loffler, v. Hofmann, Roux and Yersin, 

 Koch, Dunbar and Abbott are of the opinion that these 

 two groups of organisms are merely modified forms of the 

 Loffler bacillus. On the other hand, Hueppe, Fraenkel, 

 Escherich, Spronck and Trurnpp, among others, belonging 

 to what is called the separatist school, hold that these two 

 groups of organisms are entirely different from the L,6ffler 

 bacillus, and that diphtheria is always produced by viru- 

 lent diphtheria bacilli, and that these two groups of organ- 

 isms never increase in virulence to such an extent as to pro- 

 duce diphtheria. Most of the later investigators are ready 

 to accept the teaching of the separatist school, by the light 

 of the more definite methods now being employed. 



From the results of my studies of these organisms I have 

 reached the conclusion that we have to deal with a large 



