and sold for
fertilizer."

"Is it the fresh water that kills them?"

"No," was the reply; "that is one of the most curious features of the
life-history of the Pacific salmon. As soon as the fish are nearly ready
for spawning, all their digestive parts shrivel up, so that they can't
eat. In the male salmon, too, the end of the upper lip turns into a sort
of hook so that the fish can't even open his mouth wide enough to eat
anything. Then in the fresh water their scales turn slimy and, as they
often get injured trying to leap falls and rapids, all sorts of skin
diseases attack them. A salmon in the upper reaches of the Columbia
headwaters is a pitiful wreck of the magnificent fish that entered it to
spawn."

"Do they go far?"

"As much as a thousand miles," was the reply. "The quinnat and blue
back--or the spring and the sockeye, as they are generally known, take
the long journeys, but the silver or coho, and the humpback and dog
salmon keep to the small streams near the sea. The young fry cannot live
in salt water and the instinct of the salmon is to swim up-stream as far
as possible, no matter what obstacle is in the way. When they have gone
to the very limit, the salmon make pits and holes in the gravel and sand
at the bottom of the stream for nests, and drop the eggs in these. The
male salmon immediately afterwards floats over the nests and does his
share in making sure that the eggs will hatch out."

"How big are the salmon?" asked the boy.

"You'll have a chance to see," the professor answered, as he swung the
canoe in to the wharf, at the state hatchery station, "because we're
going to measure the ones we tag this morning."

The foreman and one of the men of the station were waiting for them in a
good-sized motor boat, towing behind which was a curious-looking affair
composed of two small barrels fastened together by long slats.

"Don't you know what that is?" queried the professor, noting Colin's
puzzled look.

"No, sir."

"That's a live car. The barrels at each end have enough water in them to
sink them to a certain depth. Then the slats, as you see, are nailed
two-thirds of the way around the barrels, leaving just enough space for
the water to flow in and out freely. They put the fish in that to tow
them home alive. The slats are better than netting because sometimes the
fishes catch their scales in the meshes and get hurt."

The run to the fish-trap was made in a few minutes, and the boat went
in