DIPHTHERIA BACILLUS. 377 
in a very few cases in which careful cultures revealed 
no diphtheria bacilli. These, if not true diphtheria, 
must be considered very exceptional cases. 
Bacteriological Diagnosis. From the above it is appar- 
ent that fully developed characteristic cases of diph- 
theria are readily diagnosticated, but that many of the 
less marked, or at an early period undeveloped, cases 
are difficult to differentiate the one from the other. 
In these cases cultures are of the utmost value, since 
they enable us to isolate those in which the bacilli are 
found, and to give preventive injections of antitoxin 
to both the sick and those in contact with them, if this 
has not already been done. As a rule, cultures do not 
give us as much information as to the gravity of the 
case as the clinical appearances, for by the end of 
twenty-four to forty-eight hours the extent of the dis- 
ease is usually easy of determination. The reported 
absence of bacilli in a culture must be given weight in 
proportion to the skill with which the culture was made, 
the suitableness of the media, and the knowledge and 
experience of the one who examined it. 
Diphtheria does not occur without the presence of 
the diphtheria bacilli; but there have been many cases 
of diphtheria in which for one or another reason no 
bacilli were found in the cultures by the examiner. 
In many of these cases later cultures revealed them. 
In a convalescent case the absence of bacilli in any one 
culture indicates that there are certainly not many 
bacilli left in the throat. Only repeated cultures can 
prove their total absence. 
TECHNIQUE OF THE BACTERIOLOGICAL DIAGNOSIS. 
Collection of the Blood-serum and its Preparation for Use 
in Cultures. A covered glass jar which has been thor- 
