METHODS OF DIAGNOSIS. 349 



the membrane is confined to the trachea the bacilli are 

 often present in the secretions of the pharynx, and may be 

 obtained from that situation by swabbing it with cotton 

 wool (non-antiseptic) or by any other means convenient, 

 the swab being put into a sterile tube or bottle for trans- 

 port. 



The means for identifying the bacillus are (a) By 

 microscopical examination. For microscopical examination 

 it is sufficient to tease out a piece of the membrane with 

 forceps and rub it on a cover-glass, or if it be somewhat 

 dry a small drop of distilled water should be added. The 

 films are then dried in the usual way and stained with any 

 ordinary basic stain, though methylene-blue is on the whole 

 to be preferred, used either as a saturated watery solution 

 or in the form of Loffler's solution. After staining for two 

 or three minutes the films are washed in water, dried, and 

 mounted. As a rule no decolorising is necessary, as the 

 blue does not overstain. Any secretion from the pharynx 

 or other part is to be treated in the same way. The value 

 of microscopical examination alone depends much upon 

 the experience of the observer. In some cases the bacilli 

 are present in characteristic form in such numbers as to 

 leave no doubt in the matter. In other cases a few 

 only may be found, mixed with large quantities of other 

 organisms, and sometimes their characters are not suffi- 

 ciently distinct to render a definite opinion possible. 

 We have frequently obtained the bacillus by means of 

 cultures, when the result of microscopical examination 

 of the same piece of membrane was non-conclusive. As 

 already said, however, microscopical examination alone 

 is more reliable after the observer has had experience in 

 examining cases of diphtheria and making cultures from 

 them. 



(ft) By making cultures. For this purpose a piece of 

 the membrane should be separated by forceps from the 

 pharynx or other part when that is possible. It should be 

 then washed well in a tube containing sterile water, most 

 of the surface impurities being removed in this way. A 



