74 Thirtieth Annual Meeting- 



V(,'rv iiii})ortfVnt factor in the transmission of disease, perhaps the 

 determining factor in its control. The fisli are crowded from 

 the standpoint of disease though not from that of aeration. One 

 naturally wonders whether wild trout ever suffer this disease. 

 The attempt has heen made to follow the history of trout distri- 

 huted from the hatchery, hut no evidence of mortality could he 

 obtained. In the wide range afforded by the natural streams lies 

 the safetv of the wild fish. Yet it will not be very surprising if 

 the disease is sometimes found in the trout streams. 



This remedy, then, is probably a preventive remedy. It is 

 difficult to believe that any with the disease well established 

 could have recovered. It is a success, nevertheless, so far and so 

 long as it is able to check and prevent this disease, and it has 

 done so in the few instances in which it could be applied. But 

 such ponds as these must of course be limited in size and their 

 ultimate infection is extremely prol^ible, if not certain. They 

 will then proi^agate the disease instead of checking it. 



There is a class of predisposing causes. The explanation, or 

 rather supposition, concerning the original entrance of infec- 

 tion regards it as a comparatively rare accident, and attributes it 

 to no factor which could have been readily foreseen and con- 

 trolled. A number of such factors have suggested themselves as 

 possible explanations of the trouble with the brook trout : — food, 

 water, lack of aeration in the water, in breeding, and the general 

 artificial conditions which may lie summed up as continued 

 domestication. Some of these could actually convey infection, 

 as the food or water, and predispose at the same time. But the 

 others are predisposing causes only, where they have any influ- 

 ence at all. They are not efficient causes. The distinction is an 

 important one because on it may hinge the future of brook trout 

 culture. As for inbreeding there is probably no such thing in 

 the sense of close consanguinity in which it is used with higher 

 animals. If water should lack slightly in aeration, if hard water 

 is of any disadvantage, if small ponds without vegetation arc 

 unfavorable, none of these things would express itself as an infec- 

 tion. But they could, singly or combined, predispose to such 

 infection, and might be so important as predisposing causes that 

 they determine the attack of disease. But the predisposition and 

 the ]u-(^sence of disease germs must coincide. It is proposed to 



