292 MICROBIOLOGY 



the cause of a serious disease affecting brook trout in certain 

 parts of the country. 



Morphology. This organism varies much in size when 

 grown in different media. Marsh refers to it as pleomorphic, 

 stating that on agar it is spherical, with a diameter of 0.5 to 

 1 fi. In liquid media it is elongated. In bouillon the pre- 

 dominating rods vary from 1 to 2.3 //, in length and from 0.4 

 to 0.8 fjL in width. It appears frequently as a diplo-bacterium. 

 In the blood of the diseased trout, it is from 0.5 to 1 /x long, 

 with rounded ends. It does not produce spores. A capsule 

 has not been demonstrated. 



Staining. It stains readily with the ordinary aniline 

 dyes. Thionin and methylene blue give excellent results. By 

 the Gram method it retains its stain in part. The iodine has 

 some fixing power with the gentian violet. 



Cultivation. This organism grows readily on the ordi- 

 nary nutrient media, with a reaction of +0.5 to phenol- 

 phthalein. It grows slightly or not at all at +1.5. It multi- 

 plies at a low temperature. 



Agar. At +0.5 moderate abundant growth appears of a 

 grayish white color which later becomes a grayish brown. A 

 soluble pigment appears in about three days which diffuses in 

 the medium but does not reside in the growth itself. It is of 

 a reddish brown shade which becomes a dark brown in from 

 two to three weeks. 



Gelatin. In gelatin an abundant growth occurs accom- 

 panied by liquefaction. At first it is crateriform but later it 

 becomes horizontal. 



Blood serum. Blood serum liquefies along the line of 

 visible growth. This becomes a dark brown color and the 

 slanting portion liquefies. 



Potato. No growth on acid potato. On neutralized po- 

 tato there is a visible growth on the third day which appears 

 as a faint growth elevated above the surface of the potato. 



Bouillon. A marked growth appears after 18 hours, 

 clinging to the sides of the tube. The liquid remains clear. 

 In about 5 days, a delicate pellicle forms and flocculi are dis- 



