MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 821 



and ultimately heal. In the deeper subcutaneous tissues there is a 

 tendency to abscess formation. Small nodules or tubercles commonly 

 appear in the lungs of affected horses. These vary in size from millet 

 seed to as large as garden peas. Various degrees of broncho-pneumonia 

 appear and more or less pleurisy. 



Bact. mallei shows no flagella and is non-motile. It is a small bacterium 0.25^ to 

 o.4ju thick by 1.5/4 to 3/1 long with rounded ends (Fig. 172). Spores have not been 

 demonstrated. It is generally single. Coccus forms sometimes appear and even 

 short threads when grown on certain media; e.g., potato. It decolorizes by Gram's 

 method and is not easily stained by aqueous, alkaline aniline dyes. This bacterium 

 grows fairly well between 25 and 42 on potato, glycerin agar, or blood serum. The 



, 

 . 



( 



: 1 



's- 





1000. 



FIG. 172. Bacterium mallei. From pure culture on glycerin agar. X 



(From Migula.} 



guinea pig gives a reliable diagnosis by inoculation, showing a diagnostic reaction 

 within four or five days. Diagnosis may also be confirmed by the agglutination test 

 in dilution of about i : 800 or more and by the complement fixation test. Satis- 

 factorily stained in tissue section by Kuehn's carbol-methylene blue. Its growth is 

 limited at an upper range of about 42. Bact. mallei is difficult to isolate by culture 

 methods being a slow grower and easily lost beside faster growing organisms. It 

 can be better isolated by guniea-pig inoculation. In growth it is both aerobic and 

 anaerobic, but better under aerobic conditions. 



The virus escapes from the body in various ways. Elimination 

 is most common in morbid discharges from the nose, pharynx, trachea , 

 and in pus from farcy buds and abscesses. 



Bact. mallei may be spread directly from the diseased animal to the 

 susceptible animal, or the dissemination may be by way of intermedi- 

 ate objects; e.g., troughs, feed boxes, water pails, etc. It is easily killed 



