406 DIPHTHERIA 



with caution. Granules staining black are not peculiar to the diphtheria 

 bacillus. Some cocci, often giving a metachromatic reaction with 

 methylene-blue, may be stained black ; and other bacilli may contain 

 such granules. A not uncommon organism with such a character occurring 

 in the throat is a strepo-bacillus with square ends ; it has no resemblance 

 to the diphtheria bacillus in a methylene-blue preparation, but when 

 stained by the Neisser method may give an appearance very like that 

 organism. On the other hand, a culture of Hofmann's pseudo-diphtheria 

 bacillus (p. 415) reacts negatively with Neisser's stain : at most a. few 

 scattered granules may occur in the preparation, but the bacilli have not 

 the beaded appearance. It will be found a good working plan to use the 

 Neisser stain only after finding bacilli in a film from a serum culture 

 stained by methylene-blue, which present the features of the diphtheria 

 bacillus. Such bacilli should react positively to the Neisser stain before 

 being accepted as such. The stain is of special service in the case of the 

 smaller forms of the diphtheria bacillus, the details of whose structure 

 are imperfectly differentiated by methylene-blue. And again when the 

 diphtheria bacilli are scanty they may be overlooked in a methylene-blue 

 preparation, whereas they are more readily detected in a. Neisser pre- 

 paration. 



AH true diphtheria give the characteristic appearance with the Neisser 

 stain, but it is of importance to observe that some hard waters interfere 

 with the reaction. , In such circumstances distilled water ought always 

 to be used for washing the preparations. 



Powers of Resistance, etc. — In cultures the bacilli possess 

 long duration of life ; at room temperature they may survive 

 for two months or longer. In the moist condition, whether in 

 cultures or in membranes, 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 importance, as they show that the 

 contagion of diphtheria may be preserved for a long time in the 

 dried condition. 



Effects of Inoculation. — In considering the effects produced 

 in animals by experimental inoculations of pure cultures, we 

 have to keep in view the local changes which occur in diphtheria, 

 and also the symptoms of general poisoning. 



As LSffler stated in his original paper, inoculation of the 

 healthy mucous membranes of various animals with pure cultures 

 causes no lesion, but the formation of false membrane may 



