196 
Diseases of Fish 
seared with a red hot seeker 1 , a ster ile platinum needle introduced, and 
sterile sloped tubes of peptonised fish gelatine were inoculated. The 
tubes inoculated from the seven infected fish showed a free growth of 
bacterial colonies in the course of a few days, whilst the one inoculated 
from the remaining fish, which was free from Gystidicola, remained 
sterile. At least twelve different species of bacteria were present, 
distinguishable by their shape, form and colour of the colonies, powers of 
liquefying gelatine, staining reactions, etc. 
The 2 fas from the swim bladders of two of the infected trout was 
o 
collected and an analysis gave 
Carbon dioxide (absorbed by potash) l’5°/ 0 
Oxygen (absorbed by potassium pyrogallate) 0'0°/o 
Nitrogen (by difference) 98'5°/o 
These fish had been caught and allowed to die in the air, so it is 
possible that any oxygen present during life may have been used up 
during the process of asphyxiation. Mr F. G. Richmond, of the Surrey 
Trout Farm and United Fisheries Co. Ltd., kindly sent me some healthy 
fish, uninfected with Cystidicola, for purposes of comparison : cultures 
from the swim bladders of these fish in every case remained sterile. It 
would thus seem probable that bacterial infection may be conveyed by 
Cystidicolae in their migration into the swim bladder of the trout, and 
it is possible that death may be caused by the introduction of pathogenic 
organisms in this manner. It is easily conceivable that any agent 
causing acute inflammation of the swim bladder, with the consequent 
dilatation of its blood vessels, would produce excessive liberation of 
dissolved gases from the blood, and thus by undue distention of the swim 
bladder disturb the equilibrium of the fish. 
With regard to the mode of entry of the parasite, it is probable as 
Shipley ( loc. cit.) suggests, that they enter along the ductus pneumaticus, 
but it is also possible that in some cases they migrate directly from the 
intestine. I recently examined a roach containing Cystidicolae both in 
the intestine and swim bladder, in which the parasite could be seen in 
various stages of development encysted in the intestinal wall, mesentery, 
and subperitoneal tissue, and so apparently making its way from intestine 
to swim bladder directly through the tissues. 
