DIPHTHERIA BACILLUS. 351 
Pseudodiphtheria Bacilli. Beside the typical bacilli 
which produce diphtheria toxin and those which do not, 
but which, so far as we can determine, are otherwise iden- 
tical with the Léffler bacillus, there are other bacilli 
found in positions similar to those in which diphtheria 
bacilli abound, which, though resembling these organ- 
isms in many particulars, yet differ from them as a class 
in others equally important. The variety most preva- 
lent is rather short, plump, and more uniform in size 
and shape than the true Léffler bacillus (Fig. 45). On 
blood-serum their colony growth is very similar to that 
of the diphtheria bacilli. The great majority of them 
in any culture show no polar granules when stained 
by the Neisser method, and stain evenly throughout 
with the alkaline methylene-blue solution. They do 
not produce acid by the fermentation of glucose, as 
do all known virulent and many non-virulent diph- 
theria bacilli; therefore, there is no increase in acidity 
in the bouillon in which they are grown during the 
first twenty-four hours from the fermentation of the 
meat sugar regularly present. They are found in vary- 
ing abundance in different localities in about 1 per 
cent. of the normal throat and nasal secretions, in New 
York City, and seem to have now at least no con- 
nection with diphtheria; whether they were originally 
derived from diphtheria bacillus is doubtful; they cer- 
tainly seem to have no connection with it now. They 
never produce diphtheria toxin, and to them properly 
has been applied the name pseudodiphtheria bacilli. In 
bouillon they grow, as a rule, less Juxuriantly than the 
diphtheria bacilli. Some of the varieties of the pseudo- 
diphtheria bacilli are as long as the shorter forms of 
the virulent bacilli. When these are found in cultures 
