324 A MANUAL OF BACTERIOLOGY 



cult to apply on account of the coherence of the growth, 

 is somewhat erratic with different strains, and is of no 

 practical value in the diagnosis of the disease. For the 

 same reasons, the agglutination reaction is of little use 

 for the recognition of the organism and for distinguish- 

 ing it from the so-called " pseudo-diphtheria " bacilli. 

 Havens x finds that by agglutination diphtheria bacilli 

 can be divided into two groups, but the two groups 

 exhibit no differences as regards morphology and patho- 

 genic ity. 



The Klebs-Loffler bacillus retains its vitality in cultures 

 for a month, and when dried for three or four weeks. 

 According to Welch and Abbot, it is destroyed in ten 

 minutes by a temperature of 58 C. It is readily des- 

 troyed by antiseptics when in culture, but in the mem- 

 brane it is difficult to find an agent which will penetrate 

 and kill the bacilli beneath the surface. 



The clinical diagnosis of diphtheria presents many 

 difficulties, and considerable assistance may be derived 

 from a bacteriological examination. The diagnosis is 

 based on the presence or absence of the Klebs-Loffler 

 bacillus, either in smears or in cultivations made from 

 the membrane or secretion (see p. 347). This method is 

 of very real assistance in doubtful, and especially in mild, 

 cases, which clinically it may be very difficult to decide 

 whether they be diphtheritic or no. The mild cases are 

 those which it is of the greatest importance to identify, 

 especially in schools, for if not recognised the patients 

 may go about and prove a source of infection to all around. 

 The method also affords valuable evidence as to when 

 a case can be considered free from infection ; so long as 

 bacilli are present in the throat infection must be possible, 

 and the length of time for which they may occasionally 

 persist is remarkable. In 20 per cent, of the cases the 



1 Journ. of Infectious Diseases, vol. xxvi, 1920, p. 388. 



