10 
(BULLETIN OF THE BUBBAU OF FISHERIES 
So far as known, the disease at present occurs in only one pond, a small natural 
lake of some 10 acres, situated on the property of Dr. L. C. Jones, of Falmouth, 
Mass. Doctor Jones first observed the tumors and submitted specimens to Mr. 
Edwards. I owe him many thanks for assistance in obtaining material and for 
various observations. 
GROSS DESCRIPTION OF THE TUMOR 
In the younger stages the timiors appear as intensely black areas of variable 
size and form in the skin of the fish (figs. 1, 2, 3, and 4). With later development 
these areas become thick and warty looking, with a very irregular surface, which 
sometimes, especially on the lips, may be fimbriated (fig. 4). Though at first the 
skin is only slightly thickened (figs. 1 and 7), the tumors may eventually rise 6 
or 8 millimeters, or even more, above the level of the surrounding skin (fig. 3). 
They are soft to the touch and, in older tumors, the slightest pressure causes the 
extrusion of any inky black fluid. This color, as will be seen later, is due to the 
presence of enormous numbers of a minute black coccoid bacterium. 
Any part of the skin may be affected, but the tumors are more commonly found 
on the fins and lips, parts which are especially subject to abrasion and are thus 
exposed to direct infection. In the majority of cases the skin on the outside of 
the body only is affected, but not infrequently tumors on the lips spread to the 
inside of the mouth (fig. 4, tumor on upper jaw). Vinal Edwards told me that he 
had seen one specimen in which the tumor had extended across the roof of the 
mouth and down the esophagus into the stomach. I observed one case in which 
the tumor, originating on the side of the body near the pectoral fin, had spread for- 
ward through the branchial chamber, involving part of the gUls, and extended across 
the floor of the mouth to the lower jaw. In one case a tumor originated on the roof 
of the mouth. 
Development proceeds so slowly that the rate of growth has not been deter- 
mined. The tumors have been observed in all stages of development, from smaU 
spots less than 3 milhmeters in diameter to areas involving more than one-third of 
the skin of the fish, and from cases in which the skin was scarcely thickened to 
those in which the tumor projected 8 or 10 millimeters above the natural surface. 
As a rule the larger tumors are more mature and much thickened; but this does not 
necessarily follow, for I have seen cases in which a tumor covering several square 
inches was scarcely raised above the surface (fig. 1) and others in which the tumor 
was as high as its diameter. 
In spite of the tendency to spredd laterally, there is no evidence of metastasis, 
and the deeper tissues beneath the tumor do not seem to be invaded; at least, in 
none of the material sectioned is there any evidence of such an invasion below the 
lower layer of the dermis, except that in older tumors the connective tissues between 
the muscles may be involved to some extent. Even in these cases the disease does 
not appear to penetrate to any considerable depth. On the fins the tumor frequently 
affects the entire substance, and a tumor originating on one side will penetrate to 
the opposite side. Perhaps this is to be expected, since the fins consist almost 
entirely of connective tissues. 
