PSEUDODIPHTHERIA BACILLUS. 407 



Inasmuch as the serum of the patient does not 

 develop agglutinins, the agglutination test is of 

 no value for the recognition of the disease. If ani- 

 mals are immunized with the bacillus, agglutinins 

 are said to be formed. The serum of such an ani- 

 mal may be used for the identification of a culture 

 made from the throat, but this would have no 

 practical value, for the diagnosis may be estab- 

 lished by the ordinary bacteriologic methods much 

 more quickly and satisfactorily. It is difficult to 

 obtain a homogeneous suspension of the bacillus 

 for the agglutination test. 



Microscopically and culturally the bacillus of 

 diphtheria can be distinguished with difficulty 

 from a variety of other organisms which belong to 

 the same group, and which are called pseudodiph- 

 theria bacilli. The latter are frequently found in 

 diphtheritic throats, but occur also in the upper 

 air passages and conjunctiva in the absence of all 

 lesions. On the whole, they are non-pathogenic, 

 but occasionally a culture is found which causes a 

 subcutaneous infiltration at the point of injection 

 in an experimental animal. Hamilton cultivated 

 one which was distinctly virulent for animals. Their 

 pathogenicity, however, is altogether different 

 from that of the diphtheria bacillus inasmuch as 

 diphtheria antitoxin does not protect against them 

 nor do animals which are immunized with pseudo- 

 diphtheria bacilli become immune to the toxin of 

 diphtheria. The Bacillus xerosis, which is thought 

 by some to be the cause of xerosis conjunctivas, 

 but which is also found under normal conditions, 

 is a pseudodiphtheria bacillus. The animal experi- 

 ment is the only positive means of differentiating 

 the true from the pseudodiphtheria bacilli. Some 



