338 



DIPHTHERIA. 



Staining. They take up the basic aniline dyes, e.g., 

 methylene - blue in watery solution, with great readiness, 

 and stain deeply. They also retain the colour in Gram's 

 method. 



Powers of Resistance, etc. In cultures the bacilli 

 possess long duration of life. Even when kept at 37 C. 



for one or two months 

 they may be shown by 

 subcultures to be still 

 alive ; at the room 

 temperature they sur- 

 vive still longer. In 

 the moist condition, 

 whether in cultures or 

 in membrane, they 

 have a low power of 

 resistance, being killed 

 at 60 C. in a few 

 minutes. On the 

 _ other hand, in the 



FIG. 86. Involution forms ot the diph- dry condition they 



theria bacillus ; from an agar culture of seven have great powers of 



endurance. In mem- 

 brane which is per- 

 fectly dry, for example, they can resist a temperature of 98 

 C. for an hour. Dried diphtheria membrane, kept in the 

 absence of light and at the room temperature, has been 

 proved to contain diphtheria bacilli still living and virulent 

 at the end of several months. The presence of light, 

 moisture, or a higher temperature causes them to die 

 out more rapidly. Corresponding results have been 

 obtained with bacilli obtained from cultures and kept on 

 dried threads. These facts, especially with regard to 

 drying, are of great importance, as they show that the con- 

 tagium of diphtheria may be preserved for a long time in 

 the dried membrane. It follows, of course, that cultures 

 can be readily obtained from membrane even after it has 

 been dried. 



with carbol-thioiiin-blue. x 1000. 



