104- Pub, Puget Sound Biol. Sta. Vol. 2, No. 39 



The treatment of these acids with limestone has been proposed. The 

 acid effluent consists of nitric and sulphuric acid. The calcium sulphate 

 produced by running the acids over limestone would be precipitated on 

 account of its practical insolubility. The question of the effect of calcium 

 nitrate on marine animals remained to be investigated. A few experiments, 

 in which a small amount of calcium nitrate was added to sea-water running 

 into one end of the gradient tank, showed that the calcium nitrate raised 

 the pH of the water and both the viviparous perch and herring were positive 

 to it as shown by graphs 6 and 7 in chart 1. 



4. General discussion 



These investigations while incomplete and faulty in that they could 

 not deal with the most sensitive stage in any of the fishes which were 

 investigated, indicate clearly that the use of SOg is preferable from the 

 standpoint of organisms to the use of sulphuric acid; that its greater 

 toxicity is offset by the rapidity with which it leaves the effluent before 

 it is mixed with sea-water or stream water in case the introduction is not 

 directly into the sea. Unfortunately one can only estimate the possibly 

 greater sensitiveness of the younger stages of herring. Since a dilution 

 of an effluent which is 35 parts per million to one tenth, without allowances 

 for the inevitable losses into the air before such a mixture can take place, 

 gives about the minimum fatal concentration for a 2l/4-gram fish, it would 

 be surprising if a dilution to one onehundredth could have detrimental 

 effect on herring at any time, for this would fall below reasonable limits 

 of toxicity and probably also below the limits which the sense organs 

 of the fish could recognize. The concentration which appears to be about 

 the minimum fatal dose for the 2.25 gram herring is also less than the 

 weakest concentration which produced abnormal development in the egg 

 of the large red sea-urchin in the work of Miss Hall (1918). A slight 

 treatment of the effluent by some aerating process (Bartow, 1917) would 

 render feasible the use of the Miles Acid Process in the treatment of 

 sewage, and would leave intact all the benefits from the standpoint of 

 public health. It would render possible the recovery of the valuable sub- 

 stances contained in sewage, as friends of the process have claimed for it, 

 and at the same time make the prospects for an abundance of marine 

 fishes near large cities and towns infinitely better than under conditions 

 in which raw sewage is introduced directly. It is to be hoped that those 

 who saw only the profits to be gained from the sale of recovered products 

 may be persuaded to advocate the introduction of the process on account 

 of the abatement of nuisance, benefits to public health, and probable 

 benefits to fisheries. 



