BACTERIA IN DIPHTHERIA. 457 
not simply encounter bacilli which are very virulent and_bacilli which are 
non-virulent; between these two extremes there are bacilli of every degree 
of virulence.” 
Abbott, in 1891, published the result of his researches with 
reference to the presence of the pseudo-diphtheritic bacillus in 
benign throat affections. He made a bacteriological study of fifty- 
three patients, nine of whom were suffering from acute pharyngitis, 
fourteen from acute follicular tonsillitis, eight from ordinary post- 
nasal catarrh, two from simple enlarged tonsils, fifteen from chronic 
pharyngitis, one from subacute laryngitis, one from chronic laryngi- 
tis, one from rhinitis, and two from an affection of the tonsils and 
pharynx. In forty-nine cases nothing of particular interest was ob- 
served. A variety of microérganisms were isolated, and of these 
the pyogenic micrococci were the most common. 
In four cases microérganisms were found which resembled the 
Bacillus diphtheriz of Léffler in their morphology and growth in cul- 
ture media, but which proved not to be pathogenic. Abbott says : 
“The single point of distinction that can be made out between the 
organisms obtained from Cases I., III., and IV. and the true bacil- 
lus of diphtheria is in the absence of pathogenic properties from the 
former, whereas in addition to this point of distinction the organism 
from Case II. gives, as has been stated, a decided and distinct 
growth upon the surface of sterilized potato.” 
Recent authors are generally inclined to the opinion that bacilli 
which resemble the diphtheria bacilli in every respect except that 
they are non-pathogenic should be regarded as attenuated varieties 
of the diphtheria bacillus rather than as belonging to a distinct 
species—the so-called “ pseudo-diphtheria” bacillus. However, there 
are bacilli which closely resemble the bacillus of diphtheria and yet 
may be differentiated from it otherwise than by the test upon sus- 
ceptible animals. Neisser has given us a staining method which is 
especially useful in making this differential diagnosis. The culture 
of the bacillus to be tested is grown upon Loffler’s blood-serum mix- 
ture. This is solidified at a temperature of 100° C., and grown in 
an incubator at a temperature between 34° and 36°C. The staining 
of a cover-glass preparation from such a culture is effected by the 
following method: Methylene blue, one gramme; alcohol (96°), two 
cubic centimetres; dissolve and add distilled water, nine hundred and 
fifty cubic centimetres, and acetic acid, fifty cubic centimetres. From 
one to three seconds only will be required to stain the cover-glass 
preparation with this solution; it should then be carefully washed in 
water and stained in a solution made by adding two grammes of 
vesuvin to one litre of boiling water. This solution is allowed to 
cool before using, and from three to five seconds will be sufficient 
