282 



SCIENCE 



[N. S. Vol. LII. No. 1343 



LIMITING FACTORS 



The injuries enumerated are tangible values 

 whicli the water may lose. There is, how- 

 ever, the general value of the life in water 

 which is so essential to its preservation for all 

 the various uses. This life constitutes a 

 great biologic equilibrium, delicately balanc- 

 ing a very complex system of factors each 

 dependent upon the other. At any particular 

 time a certain very small factor may deter- 

 mine the condition of the water. The knowl- 

 edge of what biologists call limiting factors 

 holds the greatest constructive possibilities. 

 If this fundamental principle is thoroughly 

 grasped, it makes evident the great signifi- 

 cance of certain wastes under particular con- 

 ditions, where a limiting factor may be in- 

 volved, and it shows also the possibility to 

 save a grave situation sometimes by a simple 

 expedient. The most important study in the 

 conservation of the quality of water is thus 

 to determine the specific effect of various con- 

 taminating substances upon the limiting fac- 

 tors controlling the biologic equilibrium, and 

 by eliminating them to expand the useful 

 capacity of the streams. 



PREVENTIVE METHODS 



The scientific problems involved in the 

 treatment of domestic sewage by municipali- 

 ties have been largely solved. Methods are 

 available for the intensive biologic oxidation 

 of the organic matter so that the subsequent 

 oxygen demand on the stream may be reduced 

 to any prescribed requirements. The same 

 principles may be developed for the treatment 

 of other organic wastes from food producing 

 industries, so that there should be no excuse 

 for the depletion of that great essential con- 

 stituent of the water. Considerable improve- 

 ment can be accomplished in many cases by 

 simple changes at little cost. Damage often 

 occurs through thoughtlessness or carelessness, 

 or is due to avoidable accidents. Where the 

 attention of manufacturers has been brought 

 to the serious consequences of such hazard 

 they have been willing to take proper precau- 

 tions and construct sufficient safety devices. 

 The increased utilization of valuable by- 



products, by methods well known to industry, 

 has gone far to remove the greatest wastes. 

 Likewise there are corrective processes for 

 settling out or straining out suspended matter, 

 preventing or removing colors, tastes, odors, 

 oil films, etc., and chemical methods for re- 

 moving or rendering inocuous such deleterious 

 dissolved substances as may work injury to 

 the water. By the conservative application of 

 such methods the improvement necessary to 

 meet specified conditions can usually be at 

 tained, if not always with profit, at least with- 

 out unreasonable hardship. 



RESPONSIBILITY OF INDUSTRIES 



The responsibility lies with the industries, 

 who receive from the state the benefits from 

 the waters, to study and apply the methods 

 of treatment of their injurious wastes. This 

 has been done in the past because of the value 

 of many of the by-products, and in several 

 of the more progressive concerns laboratories 

 are constantly engaged in reclamation studies. 

 While the possibility of returns has inspired 

 most of these investigations, the knowledge 

 gained leads the way to processes for the pro- 

 tection of the waters, and, in many cases, in- 

 dustries have already realized their responsi- 

 bilities to the extent of adopting measures for 

 this purpose. The great diversity and com- 

 plexity of these processes make it impossible, 

 with the limited forces at its disposal, for the 

 state to study each individually, while the 

 extensive chemical facilities of the plants 

 themselves make them not only the resi)on- 

 sible, but the logical, places to carry out much 

 of the work. Thus will the scientific knowl- 

 edge that created the damage also assume the 

 burden of the solution of the problem of its 

 prevention. The federal government is en- 

 gaged in the study of some of the broader 

 problems of national scope and some states 

 have applied themselves to the solution of 

 certain wastes in which they are particularly 

 concerned. Where the benefits to the state 

 justify the expense, it should be a legitimate 

 function to study the problems which will be 

 of general application to many industries. 

 On the other hand, the generality of the prob- 



