530 PATHOGENIC MICROORGANISMS 



parent, slimy layer. This gradually grows darker until it has assumed 

 a deep reddish-brown hue. In using this feature of the growth diagnos- 

 tically, it must not be forgotten that a very similar appearance upon 

 potato occurs in the case of B. pyocyaneus. 



Biological Considerations. — Bacillus mallei is aerobic' Growth under 

 anaerobic conditions may take place, but it is slow and impoverished. 

 The most favorable temperature for its cultivation is 37.5° C. It 

 fails to develop at temperatures below 22° C. or above 43° C. On 

 artificial media, if kept cool and in the dark, and in sealed tubes, the 

 glanders bacillus will retain its viability for months and years. On 

 gelatin and in bouillon, it lives for a longer time than on the other media. 

 Exposed to strong sunlight it is killed within twenty-four hours. Heat- 

 ing to 60° C. kills it in two hours, to 75° C. within one hour. Thorough 

 drying kills the glanders bacillus in a short time. In water, under the 

 protected conditions that are apt to prevail in watering-troughs, the 

 bacillus may remain alive for oyer • seventy days. The resistance to 

 chemical disinfectants is not very high.^ Carbolic acid, one per cent, 

 kills it in thirty minutes, bichlorid of mercury, 0.1 per cent, in fifteen 

 minutes. 



Pathogenicity. — Spontaneous infection with the glanders bacillus 

 occurs most frequently in horses. It occurs also in asses, in cats, and, 

 more rarely, in dogs. In man the disease is not infrequent and is 

 usually contracted by those in habitual contact with horses. Experi- 

 mental inoculation is successful in guinea-pigs and rabbits. Cattle, 

 hogs, rats, and birds are immune to experimental and spontaneous 

 infections alike. 



Spontaneous infection takes place by entrance through the broken 

 skin, through the mucosa of the mouth or nasal passages. Infection in 

 horses not infrequently takes place through the digestive tract.^ In all 

 cases, so far as we know, previous injury to either the skin or to the 

 mucosa is necessary for penetration of the bacilli and the development 

 of the disease. 



Glanders in horses may occur in an acute or chronic form, depending 

 upon the relative virulence of the infecting culture and the susceptibility 

 of the subject. The more acute form of the disease is usually limited 

 to the nasal mucosa and upper respiratory tract. The more chronic 

 type of the disease is often accompanied by multiple swellings of the 



1 Loeffler, loc. cit.- ^ Finger, Ziegler's Beitr., vi, 1889. 



3 Nocard, Bull, de la soc. centr. de m^d. v6t., 1894. 



