12 
(BULLETIN OF THE BUEEAU OF FISHERIES 
down into the stomach (according to Edwards), and the origin of the tumor in the 
mouth, as observed in one case, did not favor this view. The presence of the black 
granules throughout the tumor and the growth of black colonies in culture rendered 
the idea untenable. 
That the minute black granules observed under the higher powers of the 
microscope could be bacteria did not at first seem likely. Bacteria which secrete 
any form of pigment intracelluJarly are rare, and the granules are so minute (aver- 
aging only one-third of a micron) that little could be made of them, even under the 
oil immersion, though diploid individuals were common enough. The conviction 
was finally forced upon me that we have to deal with a bacterial tumor of slow 
growth and of a rather benignant type, which, however, bids fair to destroy the 
catfish in this pond and which, if permitted to spread, may become a menace over 
a larger area. 
Cultures and inoculations were made to determine whether the organism could 
be grown or transmitted. In this work I was fortunate to have the assistance and 
advice of Dr. W. W. Browne, of the College of the City of New York, and Miss 
Helen Mitchell, of Yale Univereity, bacteriologists on the station staff for the 
summer of 1919. 
It was found very difficult to grow the organism in cultures, but a measure of 
success was achieved by combining extract of catfish tissues with agar, according 
to a commonly approved procedure of bacteriological study. The growth was so 
slow that at the end of two weeks the largest colonies were only 4 or 5 millimeters 
in diameter. Contamination of the cultures was thus almost unavoidable, though 
a few of the many cultures made were successful to the extent above indicated. 
Incubation at higher temperature did not seem to hasten the growth, and cultures 
at air temperature grew about as well. The colonies in culture have the same 
intense black color as the tumors, and, on microscopic examination, the cocci 
showed the same size and appearance. 
Inoculations of uninfected catfish of the same species from another pond were 
made by the following methods: (1) By hypodermic injection of the black fluid 
from a tumor; (2) by scraping the skin and rubbing in portions of a fresh tumor; 
and (3) by grafting portions of tumor under the skin. The catfish so inoculated 
were left at Woods Hole until the end of October, two months after inoculation, 
when they were preserved in formalin and forwarded to me. Some of these showed 
undoubted tumors of small size, indicating that the disease is directly transmissible 
(fig. 9) . Unfortunately some of the fishes were allowed to become mixed up after I 
left the laboratory, so that it is impossible for me to state whether one method was 
more successful than another, though there are specimens of all three types that 
produced tumors. 
The organism causing the tumor appears to be a very minute Coccus, and 
seems to have been hitherto undescribed. It is perfectly round; it averages about 
one-third of a micron in diameter, ranging from one-fourth to one-half a micron; 
and it secretes endogenously a black pigment. Unstained smears show the organ- 
ism, because of the pigment, as well as stained preparations. In smears the indi- 
vidual cocci are not black when viewed under the oil immersion lens, but are dis- 
tinctly dark. In mass they appear absolutely black. Diploid forms, indicating cell 
