362 DIPHTHERIA. 



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

 methylene-blue in watery solution, with great readiness, 

 and stain deeply, the granules often giving the meta- 

 chromatic reaction as described. They also retain the 

 colour in Gram's method. 



Neisser has recently introduced the following stain as an aid to the 

 diagnosis of the diphtheria bacillus. Two solutions are used as 

 follows : (a) I grin, methylene-blue (Griibler) is dissolved in 20 c.c. 

 of 96 per cent alcohol, and to the solution are added 950 c.c. of distilled 

 water and 50 c.c. of glacial acetic acid ; (/) 2 grms. Bismarck-brown 

 (vesuvin) dissolved in a litre of distilled water. Films are stained in 

 (a) for 1-3 seconds or a little longer, washed in water, stained for 3-5 

 seconds in (6), dried, and mounted. The protoplasm of the diphtheria 

 bacillus is stained a faint brown colour, the granules a blue colour. 

 Neisser considers that this reaction is characteristic of the organism, 

 provided that cultures on Loffler's serum are used and examined 9-24 

 hours after incubation at 34-35 C. The same satisfactory results are 

 not obtained in the case of films prepared from membrane, etc. 



Powers of Eesistance, 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 survive 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 dry condition they have great powers of endurance. 

 In membrane which is perfectly 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 obtained from membrane even after it has been 

 dried, a fact of some practical importance. 



