190 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



SUMMARY. 



The following may serve as a brief summary of the foregoing studies upon this 

 parasitic disease: 



(1) Two factors in particular, a protozoan parasite and the high temperature of 

 the water, caused considerable loss among the fresh-water fish in the aquaria of the 

 U. S. Fish Commission at the World's Fair in Jackson Park, Chicago. Although 

 some of the fish of the aquarium were infested with fungi, the latter were not present 

 upon many of the fish which I examined. 



(2) This ciliated protozoan, belonging to the genus Holophrya {Ichthyophthirius), 

 was imported by young catfish (Ameiurus albidus), and after a time spread to other 

 fish. 



(3) The species observed is evidently identical with Fouquet's Ichthyophthirius 

 multifiUis. 



(4) From a study of its morphology and reproduction, it agrees almost equally 

 well with Zacharias's I. cryptostomus, and as the characters upon which his species is 

 founded appear to me to be open to question, I am led to doubt : although not to 

 positively deny, the validity of his species. 



(5) I. multifiUis, as observed at the World's Fair, may multiply by simple divi- 

 sion, or by division into numerous small ciliates after becoming encysted. The two 

 modes of reproduction are, however, not sharply separated, as numerous gradations may 

 be observed in this species. This reproduction is not confined to the night time, as 

 Kerbert supposed. 



(6) The eucystment may take place either on the fish or after the parasite leaves 

 the fish. 



(7) The cyst-membrane may appear before division, or at any period up to and 

 including the 16-cell stage. 



(8) It is impracticable to try to kill the parasites while they are on the fish, for 

 liquids endurable by the fish will not penetrate the slime in which the parasites lie. 



(9) Experiments to digest this slime with pepsin or to wash it off with kerosene 

 emulsion did not meet with sufficient success to warrant recommendation at present. 



(10) The most practical method of destroying the parasite is to attack it during 

 its free stage prior or subsequent to eucystment, or during its encysted stage. 



(11) The encysted stage lasts, according to my observations, about a day; accord 

 ing to Kerbert and others, from 2^ to 4 days. 



(12) The young cells resulting from the division during eucystment swim around 

 in the water and then attack new hosts. 



(13) Placing salt in the bottom of the aquarium and allowing a constant supply 

 of fresh water seems at present to be the most feasible method of treatment. 



(14) Very weak solutions of methylen blue and eosin give good results, but have 

 the disadvantage of coloring the water. Fish can live in those solutions for a number 

 of days, but the parasites which leave the fish to reproduce are killed in a few minutes. 

 If these solutions are used, aeration must be resorted to. 



