With the growth of modern, industry the problem of the influence of polluted waters on the bionomics of fishes is becoming very important. Fortunately, biologists anticipated this and many works on the subject have appeared, especially during the last twenty-five years. The polluting substances can be divided into two main classes, namely, (i) those that are directly poisonous to organisms, e.g. gas liquor, sulphites, oils, etc., and (ii) those that give rise to poisonous substances or otherwise make the water undesirable after putrefying, e.g. organic matter in solution and the decomposing bodies of plants and animals. The substances in the first category act in a relatively straightforward manner, and numerous investigators have studied them from several aspects (Shelford, '17; Matthews, '04; Powers, Wells, '15, etc.); it is with regard to those in the second class that many questions are yet unsettled and the present communication deals. We roughly know that the effect of the putrefying substances is to increase the hydrogen ion concentration and decrease the oxygen content of water. It has also been suggested that the byproducts of putrefaction themselves may be poisonous to animals.
Effects of the hydrogen ion concentration and oxygen content of water upon regeneration and metabolism in tadpoles /
