Stueam Pollution- 31 



believing that such changes interfere with the natural existence and 

 proper reproduction of aquatic life. 



In the third place, many of the substances discharged in indus- 

 trial wastes are known to be powerful poisons, so that one is forced 

 to say in advance that their action on living organisms will be dis- 

 tinctly unfavorable. In a given case it may be that the degree of 

 dilution is so great that larger and more resistant species of plants 

 and animals are not killed outright. Yet even in these instances the 

 effects of such chemicals are injurious and the vitality of the 

 organisms is lowered, the reproduction of the species is interfered 

 with, or the sensitive stages of early life destroyed. Thus in one 

 way or another the life of the stream is stunted and slowly elimi- 

 nated until, if the process is unchecked, the stream becomes a desert. 

 These conclusions do not rest purely on inference or even on 

 imperfect field studies, but are supported and justified by experi- 

 mental work in scientific laboratories, and some of the evidence 

 secux-ed in this way will be given in a later section of this report. 



Industrial wastes constitute a large and increasing element in 

 the pollution of our streams. They form a menace to the aquatic 

 life that is most serious. There is no natural series of changes 

 which render them inert or transform them in a short time into 

 materials useful in the economy of nature. Each one offers in itself 

 a problem as to, first, its exact effect on aquatic organisms, and, 

 second, the treatment demanded to eliminate the evils it has caused. 



It should be noted as an exception to the general statements mada 

 above that industrial wastes sometimes exert a mere mechanical 

 influence on the conditions of the water-body into which they are 

 discharged. Prejudice has long existed, undoubtedly with good 

 reason, against the general habit of sawmills in earlier years when 

 they were accustomed to turn loose the waste sawdust and trust to 

 the current of a stream to dispose of it. While recent experiments 

 have shown that the particles of sawdust floating in the water are 

 not, as was formerly supposed, directly detrimental to fish, and do 

 not interfere in the least with their respiratory processes, yet there 

 remains little doubt that in other fashion the sawdust ^vaste is of 

 ominous significance for them and the other life of the stream. The 

 sawdust soon becomes water-logged and settles in thick masses as a 

 loose cover on the bed of the stream. Great areas are covered over 

 by it, all sorts of attached organisms are smothered, and the smaller 

 animals are destroyed for lack of food and shelter v Soon the mass 

 itself begins to decay, exhausting the oxygen from the water and 



