504 XJ. S. BUREAU OF FISHERIES 



In some cases instead of forming hyphae the contents of the cyst 

 may divide into a number of daughter cysts, similar to those pro- 

 duced in hyphse, by a process of endogenous budding. Later the 

 cyst wall ruptures and the daughter cysts are set free in the sur- 

 rounding tissues. Once the infection is established, the mode of 

 diffusion of the parasite within an organ is not difficult to under- 

 stand, but the means by which the infection spreads from one organ 

 to another within the host is not so evident. It seems quite reason- 

 able to assume that migration occurs through the circulatory systems, 

 either lymph or blood, but so far it has been impossible to demon- 

 strate such a process. 



As a result of the development of the parasite within the host the 

 surrounding tissues become necrotic, and in severe infections may 

 disintegrate to form a puslike material which may be eliminated 

 through an opening in the skin of the fish. 



The development of the parasite is very slow, and it probably re- 

 quires weeks or even months for it to become disseminated through- 

 out the body of the host. In many cases the multiplication and dis- 

 semination of the parasite through the tissues appears to proceed 

 gradually until every part of the body is affected and the host be- 

 comes so weakened that it eventually dies, or more probably is caught 

 by one of its numerous enemies. In some instances even badly in- 

 fected fish may completely recover and groups of parasites in various 

 stages of resorption are by no means rare. The extent, however, to 

 which normal recovery takes place is unknown at present. 



Transmission of the parasite from host to host is probably effected 

 by tlie heavy-walled cysts which are thrown off in large numbers 

 through openings in the skin of infected fish. These cysts float about 

 in the water and could readily be swallowed by another fish. There 

 is no reason to believe that an intermediate host is involved in trans- 

 mission of the infection. The evidence at hand indicates that the 

 infection is much more prevalent among herring that have been in 

 inshore Avaters for some time where there are better opportunities for 

 the spread of the parasite. Apparently fish in offshore waters are 

 usually relatively free from the disease. 



Trout diseases. — Studies on furunculosis were continued by Doctor 

 Davis at the Pittsford station. An investigation of an undescribed 

 eye disease which was quite prevalent in several lots of fingerling 

 trout was also begun. The first indication of this disease is a slight 

 congestion of the blood vessels on the lower side of the eyeball. A 

 little later irregular elevations appear on the cornea due to prolifera- 

 tion of epithelial cells. Eventually the entire cornea becomes thick- 

 ened and opaque and more or less distended due to the accumulation 

 of fluid between it and the iris. In some cases the cornea may disin- 

 tegrate, allowing the fluid to escape into the surrounding water. In 

 advanced stages of the disease the lens disintegrates and the entire 

 eyeball becomes greatly shrunken. 



Only the eyes are affected, and numerous instances were observed 

 where the fish became totally blind but were apparently perfectly 

 healthy in every other respect. The cause of the disease has not yet 

 been determined. 



It was found that the spread of the disease was checked by trans- 

 ferring the fish from hatchery troughs to outdoor raceways. After 



