DIAGNOSIS OF DIPHTHERIA 295 



3. The presence or absence of involution forms, clubbing, etc. 



4. The presence or absence of thread forms : the Klebs-Loffler 

 bacillus does not form threads. 1 



5. The presence or absence of spores : the Klebs-Loffler bacillus 

 does not form spores. 



6. Motility in a hanging drop : the Klebs-Loffler bacillus is non- 

 motile. 



7. Gram's method of staining : the Klebs-Loffler bacillus stains 

 well. 



8. The grouping of the organism : the parallel grouping of the 

 Klebs-Loffler bacillus is somewhat characteristic. The bacilli when 

 lying side by side do not seem quite to touch, while the bacilli 

 which resemble the Klebs-Loffler and show a parallel grouping 

 frequently lie much closer together than the Klebs-Loffler bacillus 

 ever does. 



9. The reaction with Neisser's or Pugh's stain (the culture must 

 be a young serum one) : the pseudo-bacillus and other bacilli do 

 not give the diphtheritic reaction (polar staining). 



10. The final test of virulence may be applied. For this pur- 

 pose the organism must be isolated in pure culture by plate cultiva- 

 tions. Two guinea-pigs, of 250-300 grm. weight, are each inocu- 

 lated with 2 c.c. of a forty-eight hours' broth culture, one receiving 

 at the same time 1 c.c. of diphtheria antitoxin. If the guinea-pig 

 inoculated with culture only dies, while the one receiving culture 

 and antitoxin lives, this is complete proof that the organism is the 

 diphtheria bacillus ; if both live no inference can be made except 

 that the organism is non-virulent ; if both die it shows that 

 the organism is virulent, but that it is not neutralised by 

 antitoxin, and therefore is not the diphtheria bacillus. In cases in 

 which bacilli persist, the test of virulence is frequently applied. If 

 the organism proves to be non-virulent, presumably the patient 

 is non-infective. Such a presumption, in the writer's opinion, 

 however, is not necessarily true. 



11. Agglutination tests are unsatisfactory and not of service. 



It occasionlly happens that a conclusion cannot be arrived at 

 without an extended investigation. 



If serum tubes are not available an egg may be used. It is 

 boiled hard, the shell chipped away from one end with a knife 

 sterilised by heating, and the inoculation made on the exposed white ; 

 the egg is then placed, inoculated end down, in a wine-glass of such 



1 Klein and others have described thread and branched forms in 

 cultures of the Klebs-Loffler bacillus in certain circumstances, but 

 these are not likely to be observed under the conditions mentioned. 



