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- 



