A MORE COMPLETE DESCRIPTION OF BACTERIUM TRUTT/E 
By M. C. MARSH, 
Assistant, U. S. Fish Commission. 
The organism here described was obtained from the blood of diseased brook 
trout at a station of the U. S. Fish Commission, at Northville, Mich., during the 
summer of 1901, and is the specific cause of the disease. The name and preliminary 
characterization appeared in Science . a 
It is a pleomorphic form which assumes on nutrient agar-agar its simplest stage, 
that of a spherical or subspherical micrococcus, with occasional forms that are greater 
in one dimension. The strictly spherical forms are of an average diameter of 0.71//, 
with extremes of 0.5 to 1.0//, which are comparatively rare. Microscopically the 
field gives the impression of cocci, but bacillary individuals are frequent and reach 
a maximum length of 1.5//. In liquid media, and in liquefying gelatin and blood 
serum, it has the form of a bacillus, and the microscopical field gives distinctly the 
impression of bacilli, while occasional spherical forms are intermingled. In bouillon 
the predominating rods are of a length from that of the diameter of a coccus up to a 
maximum of 2.35//, and 0.1-8 to 0.83// wide. The arrangement is frequently as 
diplobacilli. Many of the single rods show a slight constriction indicating their 
separation into cocci, while many give no sign whatever of such a structure. A few 
of the longer forms are slightly curved. 
In the blood and local lesions of its host, the organism is in general somewhat 
larger than when growing on artificial media, and appears distinctly as a bacillus with 
occasional scattered cocci. They grow out infrequently into filaments of a maximum 
length of 6 //, but the individuals average much less, and may be not longer than the 
diameter of a coccus, and of a width between 0.5 // and 1.0 //, with rounded ends. 
When the blood or the contents of the local lesions are plated upon agar, the resulting 
colonies are alike and the plate contains apparently a pure culture. All the colonies 
are composed chiefly of cocci, which when transferred to bouillon are transformed 
into a culture chiefly of apparent bacilli 1 >y the next day, or when inoculated into 
trout reproduce the disease and are found in the blood and lesions as bacilli. This 
pleomorphism is one of the most interesting characters of the species, and repeated 
efforts failed to reduce it to a constant form. The considerable variation in mor- 
phology in a single culture can not be removed by repeated plating, and such cul- 
tures are evidently pure, notwithstanding the variety in the form of the individuals 
which they contain. 
Science, N. S., Vol. XVI, No. 409, p. V06, Oct. 31, 1902. 
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