"The wastes investigated were obtained from the main sewer of a modern Kraft paper mill, pulping only Douglas fir. . . Even though the waste reaching the main sewer has been treated so that the content of inorganic sulfide, mercaptan, soap and black liquor is greatly reduced, it is still quite toxic . . . Salmon are killed at dilutions of 1 in 10 nearly always, at dilutions of 1 in 20 most of the time, and at 1 in 40 perhaps half the time." (from the Introduction)