326 A MANUAL OF BACTERIOLOGY 



of the bacilli is proof positive of the diphtheritic and 

 infective nature of the affection, their apparent absence 

 is not of so much value, as various circumstances modify 

 the result. Thus, the swab may not touch the infected 

 portion of the mucous membrane, either from inexperience 

 of the operator or from struggling on the part of the 

 patient. The use of antiseptic gargles or paints shortly 

 before the swabbing is taken may likewise prevent the 

 growth of the bacilli. It sometimes happens that a very 

 mixed growth is obtained in the cultures, and in such 

 cases the Klebs-Loffler bacillus may be missed. Bearing 

 such sources of fallacy in mind, and making due allow- 

 ances for them, the negative result of a bacteriological 

 examination may have considerable value in those cases 

 which clinically are doubtful. In no case where there is a 

 reasonable suspicion of diphtheria should treatment with 

 antitoxin be delayed until the bacteriological report is 

 obtained. 



The diphtheria bacillus is frequently associated in the 

 throat with other organisms, especially micrococci and 

 torulaB ; and those cases in which the temperature tends 

 to be high and the throat fetid are usuaUy a mixed infec- 

 tion of diphtheria bacilli with the Streptococcus pycgenes 

 or Micrococcus pyogenes, var. aureus. The fact of such 

 mixed infection cannot, however, be definitely decided 

 from the cultures, as these organisms may be present in 

 the mouth or throat without necessarily taking part in 

 the infective process. Nor can the severity of the disease 

 be gauged from the characters or numbers of the diph- 

 theria bacilli and other organisms present, though perhaps 

 in a series of cases those which yield practically pure 

 cultures will probably be more severe than those which 

 yield cultures with few bacilli. It has been stated that 

 the long form of the diphtheria bacillus is the most, and 

 the short form the least, virulent, the medium being 



