102 Pub. Puget Sound Biol. Sta. Vol. 2, No. 39 



pH of .025. Whether or not the addition of such acids in the sea-water 

 would prevent runs of herring to a greater degree than the introduction 

 of the sewage cannot be definitely determined, but 35 parts of sulphuric 

 acid per million diluted 100 times with sea- water would probably give 

 only a very slight reduction in pH ; and with the tendency of the fresh 

 water or more dilute sea-water to remain at the top where CO, can escape, 

 it seems more than probable that the effects of direct addition to the acid 

 would very quickly disappear through the escape of the carbon dioxide. 

 In the case of raw sewage the heavier materials settling to the bottom over 

 large areas continue to decompose, producing many toxic substances as 

 well as increasing the acidity. This would tend to prolong almost indefin- 

 itely the occurrence of acid as compared with the direct introduction. 



A considerable number of experiments were performed on the vivi- 

 parous perch, a fish of some importance for food, which lives in the shore 

 water and often occurs in considerable numbers in tide pools. This species 

 is much more resistant than the herring. Table 1 shows the resistance 

 of the perch to the conditions produced by the addition of sulphuric acid. 

 The addition of 39 parts per million which gave a pH of 6.85 did not 

 kill the fishes. They appeared in several experiments to become slightly 

 intoxicated and then to acclimatize. With the addition of 65 parts per 

 million which lowered the pH 6.3, the fishes died only after 5 hours 

 exposure. The perch thus seem to be much more resistant than the 

 herring, being about five times as resistant to the effects of sulphuric acid, 

 as shown by the comparisons of the species in table 3. They select a 

 more acid water than do the herring (chart 1, graph 2). 



Flat fishes are usually very resistant to all sorts of conditions. This 

 characteristic is probably one common to all benthos. It was only with 

 an addition of 291 parts of sulphuric acid per million that the fishes were 

 killed at all. This brought the pH down to 4.35. 110 parts per million, 

 which killed the perch in 40 minutes, had little or no effect on the flat 

 fishes during a period of 24 hours except to increase their respiratory 

 activity. Whitley found that the addition of about 40 parts of acid per 

 million, which gave a one-thousandth molecular solution of hydrochloric, 

 caused considerable mortality in one of the European flat fishes, the plaice. 

 This mortality occurred only in eggs subjected to acid immediately after 

 laying, the older stages increased in resistance very rapidly, so that he 

 referred to them as "remarkably resistant." Injury can hardly come to 

 these bottom fishes with the addition of acid as a result of the Miles 

 Process of sewage treatment. Accumulation of decomposing detritus result- 

 ing from direct introduction of raw sewage would seem to be much more 

 likely to have a detrimental effect. 



