68 Thirtieth Annual Meeting 



teria. There is no excess of white blood cells as would be the case 

 if pus were present. 



The disease is extremely fatal. Usually if the fish remain in 

 the pond in which they acquired the disease, the death rate con- 

 tinues, the number dying each day becoming fewer as the school 

 grows smaller, until the last one has turned his belly upward. 



Now, what is the nature or cause of this mortality? Is it 

 merely a question of bad hygiene, that is, not a specific disease, 

 but merely a condition due to the surroundings, or food, or un- 

 suitable circumstances ? The fish cultural conditions are all that 

 care and the application of the most approved methods can make 

 them. The disease is not a mere nuitter of hygiene but is an 

 infection, i. e., parasitic. Living organisms, foreign to the trout, 

 have obtained a foothold, inhabit and gi'ow within the body of 

 the trout and at its expense. Tlie l)lood and local lesions of the 

 affected trout contain bacteria, in some cases in great numbers, 

 and the infectious agent which causes all the trouble is l)elieved 

 to Ix' l)acterial. Proof is still wanting, but experiments are under 

 way which I hope may furnish this. 



But it may be considered established that the disease is an 

 infection, which for our present practical purposes is tlie im- 

 portant point. It is caused then by a living parasite, an ex- 

 tremely small one, — a micro-parasite, which carries on operations 

 chiefly on the inside of the fish instead of the outside. It is not 

 easy to attack successfully the parasite in this position without 

 doing violence to the fish itself, and I will put aside this part of 

 the subject for the present. Prevention is worth more than cure. 



Prevention suggests the question of the original source of the 

 infection. Where did it come from, how did it get into the trout, 

 and how may it be kept out? The original source is perfectly 

 obscure at present, and may always remain so. The presence of 

 the infection is more apparent than its origin and destiny. Yet 

 there are some general considerations which have a bearing. 

 Tliere was a time, at Northville for instance, when these epi- 

 demics did not occur. It is unlikely therefore that the specific 

 germs were normally and constantly very abundant. They were 

 either constantly present in the environs of the ponds in small 

 numbers, or at some time they became temporarily numerous. In 

 the former case their constancv, in the latter their numbers, en- 



