250 PUBLIC HEALTH BACTERIOLOGY 



BACILLUS MALLEI. 



The B. mallei is the bacillus of glanders, a disease of 

 horses, mules, and asses. Horned cattle are quite immune, 

 whilst goats and sheep are intermediate in susceptibility. 

 Guinea-pigs and rabbits can be infected by inoculation, but 

 rats are immune. 



It was first obtained in pure culture and accurately 

 studied by Loeffler and Schuetz in 1882, and from the 

 human subject by Weichselbaum in 1885. 



Description. B. mallei is a medium-sized rod (3 to 4 

 micra x 0-5 to 0-75 micron), straight or slightly curved, 

 usually with rounded ends. It is about the same length as 

 the tubercle bacillus, but distinctly thicker. These bacilli 

 show considerable variations in size, even in the same 

 culture ; and this is characteristic. They are non-motile, 

 non-flagellar, non-sporing, and Gram-negative. They 

 usually appear as single bacilli ; on rare occasions short 

 filamentous forms occur. 



Staining.- The bacilli stain rather easily, but are as easily 

 decolorized. The best results are got by staining with a 

 mordant present, and simply washing in water, and 

 drying ; in the case of tissues, dehydrating by the aniline- 

 oil method. Carbol-fuchsin and carbol-thionin-blue make 

 good stains. Loeffler's methylene-blue, followed by slight 

 decolorization in weak acetic acid, and then fifteen minutes 

 in saturated solution of tannic acid, wash, dry, and mount, 

 gives good results. As a counter-stain, I per cent acid 

 fuchsin for half a minute may be used. With methylene- 

 blue, the bacilli stain irregularly ; granular, deeply staining 

 areas alternating with unstained or faintly-stained portions. 

 This has been ascribed to degeneration, and to preparation 

 towards spore formation. It is probably a peculiarity of 

 the cell protoplasm. 



Cultures. Grows well on all media at 35 to 37 C., 

 indifferent to moderate degrees of acid or alkali. Glycerin 

 or glucose render the media even more favourable. 



On agar and on glycerin-agar : the growth is greyish 

 white to yellow. 



On gelatin : growth is slow, and greyish-white ; no lique- 

 faction takes place. 



