446 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



respect tlie refuse from wood-turniug establishments must be cousidered 

 as dangerous, for the fine particles of wood-fiber will easily adhere to 

 the gills and form a basis for fungous growth. This may easily aftect 

 the entire fish, and if a river contains a great quantity of small i)articles 

 of wood-fiber, there is danger that all the fish in it will perish. Trout 

 are particularly liable to be affected by this kind of refuse, and many 

 cool and clear brooks would contain a much larger number of these fine 

 salmonoids if there were fewer i)aper factories and wood-turning estab- 

 lishments in their valleys. If the refuse contained in the water is not 

 of a soft and flaky character, but is hard, the fish are exposed to hurtful 

 influences of another kind. One of our most prominent zoologists, the 

 late Professor Von Siebold,of Munich, has proved that fish kept during 

 continued rainy weather in a fish-tank, through which passed the water 

 of a brook rendered impure by mud containing small particles of quartz, 

 became totally blind. In this case the constant mechanical irritation 

 produced by small particles of quartz had caused inflammation in the 

 eyes of the fish. They had also received actual injuries in their gills.* 

 It will be evident that water, as well aerated as possible, and as clear 

 as possible, is the first and self-evident condition required wherever ra- 

 tional fish-culture is to be carried on. The water, however, is not merely 

 the medium of breathing, but is the bearer of food to the fish. If they 

 are to prosper and increase they need a superabundant quantity of food, 

 consisting mainly of living organisms. These in turn need food them- 

 selves. But this can be furnished only if the banks are fringed with 

 aquatic plants and if the mud settling at the bottom contains a great 

 deal of humus, so that it may form a food-supplying substratum for 

 numerous microscopic algae (Besmidiacece, &g.). All the numberless in- 

 fusoria and lower crustaceans (varieties of Cladocera and Cyclops) con- 

 tained in our waters find their food in this microscopic vegetation, and 

 are, therefore, directly dependent on it. As the young fish live princi- 

 pally on the above-mentioned crustaceans and infusoria, it is evident 

 tliat anything which causes a decrease in the vegetation of tlie waters 

 (beyond a certain degree) must exercise an injurious influence on the 

 life and increase of fish. The various organisms in nature are depend- 

 ent upon each other to a wonderful and complicated degree, and the 

 great in nature is by various ways and means connected with the smallest. 

 When we see refuse and impure fluids from a factory pass into the 

 beautiful clear water of a brook, we think in the first place only of the 

 direct injuries to which fish will thereby be exposed. But the indirect 

 injuries are much greater, because they extend not only to the present 

 generation, but to the organic conditions of life, which, if endangered, 

 will make it questionable whether any fish will in the future be able to 

 live in such water. By the settling of insoluble mineral particles nt the 

 bottom of a river its microscopic vegetation is gradually killed, and the 



* From a valuable pamphlet ou the pollution of water, by Dr. Leuckart, the famous 

 Leipsic naturalist, published by Friedrich Schell, Kassel, Ibbti, 



