G. H. Drew 
201 
sheep’s liver. A plentiful growth resulted which soon developed the 
typical sporangia of Saprolegnia ferax. 
Cultures on peptonised fish gelatine were made from the superficial 
and subcutaneous tissues of the fish and resulted in a rapid growth of 
bacterial colonies, some of which liquefied the gelatine. 
These colonies developed at first as small grey dots surrounded by a 
partially liquefied area: in later stages all the gelatine became liquefied 
and the individual colonies were indistinguishable. The colonies were 
composed of actively motile, short, thick bacilli with rounded ends, 
usually arranged in pairs, end to end. They stained readily with the 
usual stains, but did not retain Gram’s stain. Subcultures grew 
profusely in from 18 to 24 hours at the room temperature (about 
16° C.), and caused rapid liquefaction of the gelatine : they also grew 
profusely but less rapidly at 0° C. 
Peptonised fish broth, inoculated from these cultures, showed 
cloudiness throughout in from 18 to 24 hours, and developed a 
delicate pellicle on the surface which adhered to the sides of the tube. 
Sections of the subcutaneous tissues, cut perpendicular to the 
surface and stained with Ldffler’s methylene blue, showed that the 
tissues under the affected areas were crowded with the diplobacilli 
described above : in the deeper portions these diplobacilli were present 
alone, but in the more superficial parts there was a mixed infection. 
A few weeks after receiving these fish I was given the opportunity of 
visiting the Colne and of investigating the matter on the spot. I 
repeated the experiments with cultures taken from fish in the earlier 
stages of the disease and again isolated the same bacillus. 
There seems little doubt that the diplobacillus was the Bacillus 
salmonis pestis described by J. Hume Patterson in the Parliamentary 
Report on the Salmon Disease, presented by the Fishery Board for 
Scotland (1903), and that the fungus Saprolegnia ferax had attacked 
the necrosed tissue produced by the bacterial invasion. 
This combined infection is what is commonly known as the Salmon 
Disease, which produced such great mortality among salmon, trout and 
other fish in 1877, 1882, and following years. 
