402 BA CTERIOL 00 Y. 



(for there are probably several) that is enough like the 

 diphtheria bacillus to attract attention, but is distin- 

 guishable from it by ^certain morphological and cultural 

 peculiarities aside from the question of virulence. 



It is a well-known fact that many pathogenic organ- 

 isms — conspicuous among these being iniorococcMS lan- 

 ceolatus, staphylococcus pyogenes aureus, streptococcus 

 pyogenes, and the group of so-called "hemorrhagic 

 septicaemia " organisms — undergo marked variations in 

 their pathogenic properties ; and yet these organisms, 

 when found either devoid of this peculiarity, or possess- 

 ing it in a diminished degree, are not designated as 

 "pseudo" forms, but simply as the organisms them- 

 selves, the virulence of Avhich, from various causes, has 

 been modified. 



It must nevertheless be admitted that in the course 

 of microscopic examination of materials from various 

 sources, including the pharynx, one occasionally en- 

 counters micro-organisms whose morphology is so like 

 that of the genuine bacillus diphtherioe, as to create 

 suspicion, and yet they are at the same time sufficiently 

 unlike it to make one cautious in forming an opinion 

 as to their real nature. 



Through the suggestion of Neisser^ we are fortunately 

 enabled to overcome this difficulty in very large part. 

 He has found that by tlie use of a particular staining 

 method the appearance of bacillus diphtherias is strik- 

 ingly unlike that of the confusing forms. His differ- 

 ential method comprehends the following manipulations : 

 the culture to be tested should be grown upon Loffler's 

 blood-serum mixture solidified at 100° C. ; it should 



' Neisser : Zeitschrift fiir Hygiene und Infektionskraukheiten, 1897, 

 Bd. xxiv. 



