IN THE RIVER COLNE AT WATFORD. 
95 
labelled ‘ Water with coating of tar ’ was saturated with tar, and 
had a very little tar, about two drops per pint, floating on the 
surface. I find by experiment that tar when added to water soon 
seriously reduces the quantity of dissolved oxygen in the water, 
and it is oxygen on which fish, like ourselves, depend for respira¬ 
tion. In my opinion fish would be liable to be suffocated in water 
thus super-saturated with tar. The water labelled ‘ Water from 
Sedgwick’s ditch ’ possessed a strong smell of decaying vegetable 
matter and contained an unnaturally small portion of dissolved 
oxygen. I am distinctly of opinion that fish would be liable to die 
by suffocation in such water.” 
With regard to the effects of lime in the river Prof. Attfield says: 
—“ The action of lime in killing fish may be direct or indirect. 
Direct by dissolving in the water and forming an irritant caustic 
alkali to the delicate structures of fishes, just as solutions of the 
stronger alkalies, potash or soda, are irritant caustics to stronger 
animals. Indirect, because the organic matter in all fish-frequented 
waters, whenever the water becomes charged with lime, very rapidly 
absorbs the life-supporting oxygen of that dissolved air which fishes 
breathe, and of course the fish then die of suffocation. Quick-lime 
and slaked lime are identical in action simply because the quick¬ 
lime becomes slaked lime in contact with the water, 1£ lb. of quick¬ 
lime giving about lb. of slaked lime, and the latter dissolving in 
about 1000 gallons of water. Water thus limed soon absorbs car¬ 
bonic acid from the air, the lime thus being converted into chalk, 
which is harmless, and is either deposited as a sediment at the 
bottom of the water, or remains in solution when excess of carbonic 
acid is present, making the water harder than it was before.” 
As experience gained from other places may throw light upon 
our investigation, I have asked for information on fish-poisoning 
from others. Mr. George Rooper says:—“My knowledge of fish¬ 
poisoning is limited. In the south and west of Ireland the water 
in which flax is steeped is a deadly poison, and frequently the cause 
of much mischief, and I have heard that in the same localities other 
herbs are soaked and used by poachers for the destruction of fish. 
Cocculus indicus was formerly much used by poachers. Lime is a 
most destructive agent in the poachers’ hands, and is much used in 
South Wales. Its effect is the choking of the delicate machinery 
of the gills, preventing breathing and acting as would removal of 
the fish from the water. Gas-tar, naphtha, or petroleum getting into 
a river by accident or design will poison every fish with which they 
come in contact. The drainings from a lead-mine will entirely 
deprive a stream of its trout. From Frank Buckland’s experiments 
it would seem that this is owing to the silt when precipitated 
choking up and destroying the spawn. The gases generated in a 
shallow pond or lake in very hot weather are destructive to piscine 
life. I once saw a lake in Sussex the surface of which was covered 
with bubbles no doubt full of gas. I remember, too, when a boy, 
that the same occurred in Whittlesea Mere, then a lake twenty 
miles round. The fish were destroyed in millions.” 
