MacCallum. — Diseases of Fishes 157 



sea, and it seems obvious that rigid disinfection of tanks, 

 etc., would easily stamp it out. 



Many of the fish in confinement show upon autopsy a 

 great distension of the gall bladder sometimes with gen- 

 eralized jaundice. It is usually found to be due to nar- 

 rowing of the common bile duct by inflammation of its 

 mucosa, although it is sometimes caused by blocking of 

 the duct by parasites. It is not easy to give an explana- 

 tion of this. A number of examples of the peculiar affec- 

 tion of the thyroid so much studied by Gaylord, Marine 

 and Lenhart came to my attention. As is well known, it 

 is even yet a matter of dispute as to whether this enlarge- 

 ment of the gland which may affect the isolated fragments 

 of thyroid tissue scattered so widely in the tissues of the 

 fish is to be regarded as a malignant tumor or not. It is 

 at least destructive of the lives of many fish in hatcheries 

 of trout, but Marine thinks it merely a modification of 

 the gland caused by unsuitable food and over crowding, 

 and especially by lack of iodine-containing food. Gaylord 

 thinks it cancerous. 



A few more definite tumor growths have been encoun- 

 tered, one which produced a rounded protuberance on 

 each side of the dorsal fin of a Neomaenis griseits (Gray 

 Snapper) . These proved on section to be a hard fibroma 

 composed of very dense fibrous tissue with relatively few 

 cells. Two fish, a red hind and a pickerel, died after an 

 affection of about three months during which the soft 

 tissues of the lower jaw and part of the tongue were 

 wholly destroyed leaving the bones completely bare as far 

 as the angle of the mouth. This was at first thought to 

 be an epitheliomatous growth but sections of the margins 

 of the tissue showed no tumor and the nature of the pro- 

 cess is obscure. A large snook (Centropomus undecimal- 

 is) was observed for a long time in the Aquarium with a 

 large tumor on the tip of its lower jaw, which may pos- 

 sibly have been of the nature of the thyroid enlargements. 

 Unfortunately it was not studied at autopsy. Another, a 

 black grouper {Mycteroyerca bonaci) showed at autopsy 

 a firm nodular mass constricting the rectum which was 



