THE AQUARIUM AT THE WORLD'S COLUMBIAN EXPOSITION. 157 



often infested, although the bream and other sunfishes were likely to go one at a time, 

 as they weakened individually. The European carp and the common ornamental fishes 

 (golden ide, goldfish, and tench), thoroughly accustomed as they arc. to aquarium life, 

 were scarcely affected at all ; and the dogfish, the gars, the sturgeons, the striped sucker, 

 the nati ve species of carp, the burbot, the eel, and the lamprey were also practically free 

 from disease. Whitefish, although living but a short time in the aquarium, were not 

 particularly liable to the fungous disease, but seemingly died because they would not eat. 



April 28, eighty-seven young catfish (Ameiurus albidus) about 6 inches loug, just 

 received from the Potomac River, were placed in an aquarium together. Their interest- 

 ing habit of massing in the center of the tank, each one swimming slowly back and forth 

 and in and out through the school, attracted common attention to them. About six 

 weeks later it was noticed, however, that their habit had changed completely, and 

 that they now scattered everywhere, swimming restlessly about day and night, as if 

 eager to escape. At this time it was also observed that the skin of these fish was 

 covered with minute white specks, that they had ceased to feed, and were beginning 

 to die. The usual aquarium treatment for fungous disease was tried without special 

 result, and as other species near them in the aquarium had become similarly affected, 

 I began, July 10, a preliminary microscopic and experimental study of their disease. 

 The minute pimple-like specks on the skin, on the gills, and within the mouth were 

 found to contain large, spherical, densely ciliate protozoa. These were contained in 

 little cavities in the epidermal layer of the skin or mucous membrane, within which 

 they kept up an incessant rolling motion. If freed from their confinement they swam 

 about rapidly through the water, where they could be readily seen with the naked eye. 



I soon ascertained that this parasite belonged to the genus Ichthyophthinus of 

 Fouquet,* first described in Europe in 1869, and recorded there as an aquarium para- 

 site especially destructive to young trout, but infesting a number of other species 

 also. As the practical problem pressed upon us much more urgently than the scien- 

 tific one, we began without delay a series of experiments with vinegar, salt water, 

 copperas, carbolic acid, and other like substances, hoping to find some disinfectant 

 solution in which the infested fish might be dipped with the effect of killing the para- 

 site without injuring the fish. Time failing for the active and continuous work which 

 the subject demanded, I had the good fortune to secure the assistance of Dr. Charles 

 W. Stiles, of the Department of Agriculture, who was at the Exposition at the time. 

 By courtesy of Hon. J. Sterling Morton, Secretary of the Department of Agricul- 

 ture, Dr. Stiles was given leave of absence, and July 17 entered on a systematic experi- 

 mental investigation of the subject. The report which he has filed for publication with 

 this paper makes unnecessary any further account of the matter here. 



I will only add that no disinfectant substances were found practically useful. Salt 

 was the only one even recommended to us as the result of Dr. Stiles's experiments, 

 and if this were employed to the extent necessary to destroy the parasite, it com- 

 monly affected the fish more injuriously than did the parasite itself. 



*See fufusionsthiere als Haiitparasiten bei Siisswasserfischen, by F. Hilgendorf and A. Paulicki, 

 (Centralbl. f. d. med. Wisscusch. 1869, p. 33); Note sur une espece (Vinfusoires, parasites des poissons 

 d'eau douce, by D. Fouquet (Ai-ch. zopl. exper., t. v, 1876, p. 159) ; Chromatophagus parasiticus n. g. et n. 

 s}). Ein Beitrag cur I'arasitenlehre, by C. Kerbert (Nederl. Tijdschr. v. d. Dierk. Jabrg., v., 1884, p. 44) ; 

 "Manual of Infusoria," p. 530, by W. S. Kent; Bronn's "Tbier-Reicbs" Bd. i, in. Abtb., p. 1678; 

 and Ein infusorieller Hauptparasit bei Siisswasserfischen, by O. Zacbarias (Biol. Cent. 1893, p. 23). 



