Amcriran FisJicries Sorirfij. 109 



poso is concerned, ])rcvention of tliis disease. They demonstrate 

 tliis fact very clearly — that they are insuliicient to deal with it 

 as exemplified at the Xorthville Station, and in so doing they 

 make a valuahle eontrilnition to kn()\vle(|>iX' of this disease, and 

 an important step is taken in attenvpts at prevention. For the 

 idea of exclnding infection by an impervious construction fol- 

 lowed naturally from the nature of the disease and was one of 

 the very few practicable means of dealing with the problem. The 

 ponds accomplished this exclusion, for they have withstood the 

 severity of winter and are practically intact. They have ])r()- 

 tected the trout from infection contained in the earth about the 

 pond and this being insuiheient the conclusion is forced that the 

 water itself brings into the pond the bacteria of disease^ and that 

 the springs that supply the station are their source. That these 

 bacteria arise in the springs is a matter of very serious import. 

 It throws the origin of disease back to a source over which we 

 have no control. It is im])ossil)le to disinfect tliese springs. Dis- 

 infection can occur only in the superficial layer of the bottom 

 while fresh infection is constantly arising from the depths. The 

 water cannot be filtered to a germ free condition on the necessary 

 scale for practical operations. The infection cannot l)e dug out. 

 It is a natural attribute of the supply springs and I do not see 

 any means of dealing with it which allows brook trout culture on 

 the present intensive plan, i. e., many fish in a small space, and 

 at stations with infected water. 



This does not compel the al)andonment of the l)rook trout at 

 such stations, however ; at least, not as yet. The next thing to be 

 recommended is culture in comparatively large natural ])onds. 

 The chief advantage gained is the increase of s])ace, diluting the 

 infection and se])arating the fish. The more natural conditions, 

 aside from space, doubtless have their inflneiu-e also. There is 

 some past experience favorable enough to justify such a pond. 

 Mr. I?. S. Johnson of the United States Fish (*onnnission has 

 checked the disease in this way at his station at Manchester, 

 Jowa. It may be considt'red a sort of compromise with tlie dis- 

 ease because even if continuously successful, it cannot be exjjected 

 to produce as numy trout to a given outlay of space as tlie small 

 pond system. It cannot eradicate all the conditions that cause 

 the disease, and it is possible, even probable, that with continued 



