"Of course," the boy responded.
"And you know that the United States Government has an inspector at every place where cattle and sheep and pigs are slaughtered to see that no diseased animals are sold?"
"Yes," the boy answered, "I have heard of that, too."
"Since there is almost as much fish eaten in this country as there is meat," the professor continued, "Uncle Sam sees to it that no diseased fish are sold for food."
"I don't quite see how," the boy responded; "there can't be an inspector at every place where they catch fish."
"Certainly not, but as long as there is no disease among fish, there can be no diseased fish. We try to prevent the diseases. Now here, for example," he continued, "are a lot of fish that have a kind of malign growth. It comes very frequently among the trout and salmon that are artificially raised, and sometimes we find it among fish that have been reared in a state of nature, and
I have been working for some time on this and I hope this year—or at all events by next season—to be able to show the cause of the disease. That is really my problem, Colin, but the details of it are too complicated to explain easily. But you have come at a particularly good time," he continued, "because I have been wanting to do an experiment which I thought might interest you, and I waited until you came. If you like, we'll go out to-morrow."
"I should, ever so much," Colin exclaimed. "What's the experiment?"
"When the salmon come in from the sea," the professor began, "there is a great deal of hesitation among them sometimes before they go up the river to spawn, and we want to find out whether they go back to the sea again, whether they swim directly up the stream, or whether they remain in the brackish water at the mouth of the river."
"If you don't mind my saying so, what is the use of knowing?" asked Colin. "I mean, what does it matter as long as the salmon spawns?"