920 BULLETIN OF THE BUREAU OF FISHERIES. 



fario from the excellent stream of Stara Voda) — were attacked along with the 

 embryonated eggs obtained from elsewhere." The fry that Avere fed nothing 

 but live crustaceans and larvae of mosquitoes, their natural food, were infected 

 as much as those which, on account of temporary lack of natural food, were fed 

 partlv with substitutes, such as pig liver or beef and veal spleen. 



The infection must, consequently, be of the locality. The place, the water 

 and its near surroundings, must be infected, the shores harboring Costia in the 

 shape of cysts on the dry land, whence they are scattered everywhere by 

 the wind. 



Costia had already established itself at Studenec before my arrival in 1891. 

 Costiasis thus did not begin during my direction, but it spread so rapidly and at 

 last in such manner that none of the springs were safe from it. It was first rec- 

 ognized in 1904 by Dr. Ivan Robida, head of the hospital for the insane in 

 Studenec, who was fond of the sport of fishing and who in his close relations 

 with myself studied questions which interested me. By means of his micro- 

 scope (my own not powerful enough) and Dr. Hofer's book, the identity of the 

 disease germ was fixed in 1905. 



We conclude, further, that we have found the cause of the abnormal mor- 

 tality of fry in previous years, there appearing the same phenomena and 

 symptoms and course of the disease from the very beginning that had char- 

 acterized those great losses for which no cause was known from 1896 until 

 this time. I had sufficient occasion and opportunity to observe all the 

 phenomena and symptoms minutely, and likewise to remember them, for a 

 large part of the feeding fry were placed for one to three months in larger 

 hatching boxes, then in floating troughs, and in September and October in 

 large ponds in which to pass the winter, while I spent each year 180 half 

 days and 40 to 60 entire days in this establishment. 



ACCIDENTAL DEVELOPMENT OF THE PREVENTIVE METHOD. 



The radical means of preventing Costia was not " discovered, " nor even 

 "found," for it was not sought. It developed in the following manner: 



In the one-story house occupied by Doctor Robida and other physicians 

 of the insane asylum there is a tank under the roof with capacity of about 

 1,800 liters, into which was pumped water for household purposes from a spring 

 situated in the cellar of a house about 80 meters distant, if sufficient water was 

 coming to the ponds for the working of the pump. The spring in the cellar 

 and the tank are well covered and the pumped water, coming in contact with 

 the fresh air from without only by chance rifts in the cover, can not be much 



aSalmo jario from Ilidze, Bosnia, 1902; Salmo dentex (Isonzo trout) from Idria, 1903-1907, 

 inclusive. 



