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bacteria and from that moment onward, other differentiating 

 characters have been looked for. 



It would be no use to sum up everything, that has become 

 known of late years to characterize the diphtheria bacillus. 

 I should - only like to mention the most inportant. Beside shape 

 and non motility, it is in the first place its reaction on diffe- 

 rent stains, namely the irregular staining of the protoplasm 

 by anilin dyes. The well-known staining method of Neisser, 

 which makes the metachromatic bodies of Babes-Ernst clearly 

 visible, is based on this characteristic of the diphtheria bacillus. 



In the second place its reaction on Gram's staining should 

 be mentioned. Another character is found in the way in which 

 it grows on different culture media, specially the rapidity and 

 abundance of growth on LöFFLER'S serum (ox or horse serum 

 mixed to a proportion of 3:1 with glucose broth) and the 

 nature of colonies formed on it. 



As is the case with so many other bacteria, it has also been 

 tried with the diphtheria bacillus, to find typical characteristics 

 in its reaction on several carbohydrates ; especially the production 

 of acid in glucose containing media plays an important part 

 as a diagnosticum and special attention is paid to the amount 

 of acid produced. 



Is it possible now to make out with the help of these details, 

 which may be got in the way I suggested above and 

 which belong all of them to morphological or cultural proper- 

 ties, if a pure culture we are working on is one of true diphtheria 

 bacilli? In many cases, it is no doubt likely to be so, but we 

 dont get certainty, we only approach the truth and the more 

 we extend our investigation this way, the nearer we get to it. 



Fortunately there are other characters which may help us 

 somehow one way or the other. These are derived from the 

 immuno-reactions and the experiments on animals. Analogical 

 to what was taught by other pathogenic microorganisms, several 

 serological reactions were tried for diphtheria too. In the first 

 place I should like to mention the agglutination. 



If we follow the working-method, used for example in typhoid, 

 we dont get any satisfactory result. But other methods have been 

 worked out, for instance about 5 years ago in the laboratory 

 of Prof. SprONCK in Utrecht, which gave very useful results. 



