248 BACTERIOLOGY. 



a thin, dry glaze can be noticed at the point at which the 

 potato was inoculated. Microscopic examination of the 

 potato after twenty-four hours at 35°-37° C. shows a 

 decided increase in the number of individual organisms 

 planted. 



Stab and Slant Cultures. — In stab and slant 

 cultures on both gelatin and glycerin agar-agar, the 

 surface growth is seen to predominate over that along 

 the track of the needle in the depths of the media. 



Isolated colonies on the surface of either of the media 

 in this method of cultivation present the same charac- 

 teristics that have been given for the colonies. 



The growth in simple stab cultures does not extend 

 laterally very far beyond the point at which the needle 

 entered the medium. 



It is a non-motile organism. 



It does not form spores. 



It is killed in ten minutes by a temperature of 

 58° C. 



It grows at temperatures ranging from 22° C. to 

 37° C, but most luxuriantly at the latter temperature. 



Its growth in the presence of oxygen is more active 

 than when the gas is excluded. 



Staining. — In cover-slip preparations made either 

 from the fauces of a diphtheritic patient, or from a pure 

 culture of the organism, it is seen to stain readily with 

 the ordinary aniline dyes. It stains also by the method 

 of Gram, but the best results are those obtained by the 

 use of Loffler's alkaline methylene-blue solution ; this 

 brings out the dark points in the protoplasmic body of 

 the bacilli and aids thus in their identification. 



For the purpose of demonstrating the Loffler bacilli 

 in sections of diphtheritic membrane, both the Gram 



