352 JOURNAL OF SCIENCE. 
salmon rivers, and at the same time increased the quantity of | 
nitrogen supplied to them. To follow up the effect of these we 
must assume (what I think may be conceded) that the same run 
of salmon numerically takes place now as occurred sixty years 
ago. Given thena pool in Tweed, say “Gleddies Weel,’ which 
in 1822 carried a third more water than in 1882, and water with 
a larger proportion of oxygen in it, with 200 salmon in full vigor 
of life. How is it possible for the same number of fish at pre- 
sent to maintain health with a third less water, and vitiated at 
the same time by an overdose of nitrogen, delayed also, it may 
be, two months beyond their natural time of reaching that pool ? 
But there are many rivers of North Western America still un- 
affected by agriculture, and waters in New Zealand as pure, 
where this fungoid. ora similar disease is known. This may 
fairly be urged against my theory, but it is not therefore unan- 
swerable. In the long American rivers, as the Fraser, the habit 
of the salmon, S. guznuat, or S. chonicha, is the direct cause of 
the disease. For even after this fish has travelled up hundreds 
of miles from the sea and spawned, it still presses upwards, losing 
condition and strength daily, and gets scarred and bruised by 
rocks till its vitality is reduced beyond the point where it can 
throw off the attacks of fungus, and to which it eventually suc- 
cumbs, and dies covered with a mass of offensive sores. Again, 
in Queenstown Bay, Lake Wakatipu, New Zealand, where the 
water is pure and abundant, and the trout remarkably fat, this 
fungoid disease is widespread. In this case there is a total ab- 
sence of salt in the water, and all fish above a certain size are 
unable to ascend their native stream, the Town Creek, owing to 
its smallness, tospawn. These two reasons appear to me enough 
to make the trout subject to the disease, and, as a matter of fact, 
they die from it, although as yet not in great numbers. In a 
word, then, the blood of the salmon when deprived of its proper 
quantity of oxygen deteriorates, and thus so weakens the fish 
as to leave it with no vigour of life or strength sufficient to throw 
off the seeds of the fungoid disease. 
Finally, contrasting, then, the above facts—lowness of rivers, 
want of oxygen, excess of nitrogen, prolonged residence of sal- 
mon in the rivets with fungoid disease prevalent, as at present ; 
and on the other hand, plenty of water, free passage of fish, fish 
abundant and healthy, as obtained sixty years ago—and the 
conclusion is plain that the disease in Tweed, &c., is due not to 
a single specific cause, but to those connected with the altered state 
of the rivers, and that the remedy must lie in restoring these 
rivers to their previous condition so far as practicable. This re- 
storation can only be effected by the general concurrence and 
united action of all the higher and lower proprietors, assisted in 
the first outlay by a Government subsidy. In other words, com- 
pensation reservoirs must be constructed on all the tributaries of 
salmon rivers, to impound the excess of flood waters, and from 
which reservoirs it may be delivered during the dry months to — 
assist the salmon in its ascent and descent. This is the first 
