American Fisheries Society. 71 



introducing infection into tlie water. At this point it may occur 

 to YOU to ask wliy, if the cement construction is a barrier to infec- 

 tion, can it not be continued up the conduits and into the springs 

 and make the water system impregnable? The objection will as 

 readily suggest itself. As far as the conduits are concerned this 

 would be excellent, but when it comes to the spring that of 

 course must be left sufficiently open to deliver the water. These 

 openings would defeat the main purpose of the cemented spring. 

 It is a case of a little leaven leavening the whole loaf. The 

 cement here might be of some value, but if infection underlies 

 the spring the water would carry it in. If the water entering a 

 cement lined spring could be filtered free of micro-organisms 

 there would be complete protection in association with cement 

 ponds from infection through soil or water. But this degree of 

 safety cannot be attained. As for the prevention of disease by 

 the use of cement or stone, we must count on the application of 

 these to the ponds alone as so nearly covering the whole source 

 of infection as to offer reasonable hope of accomplishing the pre- 

 vention. This means that the pond infection is so large a part 

 of all the infection to which the trout are exposed, that protec- 

 tion from it will mean protection from disease, — except, no 

 doubt, the occasional outbreak. The danger of an occasional 

 outbreak is a risk which must be assumed. At Northville, dur- 

 ing the past June, the fry in the troughs in the hatchery com- 

 menced to die of the disease which was among the yearlings in 

 the ponds out of doors. This is the first time in some years that 

 ■serious trouble has occurred with the fry in troughs, and perhaps 

 the first occurrence of this particular disease in the troughs. KX 

 first this seems to militate against the pond theory, for the 

 trougli supply water comes directly from a large s])ring above 

 the ponds. But this spring is practically a fish pond, for trout 

 have been kept there from time to time, and while disease has 

 not been noticed there it is not improbable that it has occurred. 

 There is always considerable loss from such ponds, part of which 

 is due to depredations. But it must be remembered that fish 

 dead or dying from disease would be apt to bo quickly appro- 

 priated by birds and animals, or to be lost to sight in the vegeta- 

 tion, the conditions in this respect being quite different from tho 



