CULTURAL AND BIOLOGIC PROPERTIES 309 



grows rapidly, and the medium after twenty-four hours shows a slight 

 uniform clouding; later a whitish, slimy sediment is formed without 

 clearing of the supernatent fluid. If the fluid is not disturbed a 

 whitish, slimy surface pellicle is also formed, and even after this has 

 sunk to the bottom a white ring or margin remains at the circum- 

 ference of the surface and the glass. On slightly acid glycerin agar 

 the organism develops well, but there is nothing characteristic about 

 the growth. The colonies are first flat, dull white or grayish, trans- 

 lucent; later they become somewhat yellowish or perhaps even some- 

 what reddish yellow. The colonies rapidly become confluent in the 

 incubator, slowly at lower room temperatures. The organism grows 

 well on horses' and sheep's blood serum, and not so well on cattle 

 blood serum. The colonies after about three days appear as yellowish, 

 translucent drops on the surface of the coagulated serum. They 

 possess a tenacious, slimy, viscid consistency. After eight to ten days 

 the growth on blood serum becomes opaque and grayish white. On 

 potatoes the growth of the Bacillus mallei is most characteristic; it 

 appears after about two days as a delicate, yellowish, translucent 

 cover, and on the third day assumes an amber color. After six to 

 eight days the growth has become quite abundant. It is now opaque 

 and has lost most of its transparency, being reddish yellow in color. 

 The surface of the potato not covered by the growth has assumed 

 a faintly green hue. This zone, however, may not be very noticeable 

 or it may be yellowish green or brownish green. In using potatoes 

 for the cultivation of the Bacillus mallei it is important to select such 

 as are not too acid, or, still better, to correct the acidity before sterili- 

 zation. Potatoes which have been frozen or which have begun to 

 germinate should not be used, because they are likely to contain 

 sugar from which the Bacillus mallei forms acids. It is best to 

 immerse the disks or pieces of potato, after washing and peeling, for 

 one hour in a 0.5 to 0.7 per cent, solution of bicarbonate of soda and 

 then to sterilize them. In this manner a material of not too high 

 acidity is obtained. Certain other bacteria when growing on potato 

 form a growth more or less similar to that of the Bacillus mallei. The 

 most important of these is the Bacillus pyocyaneus. This organism 

 produces a yellowish-brown growth, which, however, is not trans- 

 parent; older colonies also exhibit a mother-of-pearl luster not shown 

 by the Bacillus mallei. A simple test to differentiate between the 

 two organisms when grown on potatoes and closely resembling each 

 other is to spread some of the growth on a piece of filter paper and 

 expose it to ammonia vapor. If the growth is Bacillus pyocyaneus 

 a characteristic bluish-green color at once appears; this is not shown 

 when the growth is Bacillus mallei. An evidently rare pseudomalleus 

 bacillus, discovered by Babes, forms a growth like the genuine glanders 

 bacillus on potatoes, and can be accurately differentiated only by 

 animal experiments. In guinea-pigs, field mice, and cats it produces 

 local processes only, but kills rabbits. 



