American Fisheries Society. 163 
ean call by courtesy a lake. A lake of 15 or 20 acres will show 
as thick a layer as that. So that you have got to go deeper than 
that for cold water. If you think of using a lake in the way you 
speak of, you ought to visit the lake in August or in September, 
and ascertain what the gas conditions are in the lower water. In 
the cool water from Lake Mendota, the fish will die quicker than 
on land. If you put a fish into this water and keep him where he 
cannot get his mouth out, and get air, and he will keep his gills 
working with the result that the oxygen will get out of his blood 
instead of going into it; whereas, if he were out on land, he 
would simply wait until he had used up himself all the oxygen 
which he had. There are other gases which develop in the lower 
water, but so far as I know, those gases are not directly poison- 
ous to animal life. The carbon dioxide does not seem to affect 
the animal life directly. But the question of the amount of oxy- 
gen is very important. You could pump water out of the deeper 
waters of Green Lake, for instance, to supply a hatchery and 1: 
would be perfectly satisfactory, so far as oxygen is concerned 
though I am not sure that you would not be troubled even in that 
water with an excess of nitrogen. 
Mr. Titcomb: That would readjust itself quickly in flowing 
res) 
on the surface. 
Dr. Birge: Yes, but the water would also become warm. Ii 
is a question whether you could get rid of excess nitrogen with- 
out warming the water more than you want to. 
Mr. Titcomb: On a rapid current a stream does not warm 
up very quickly. 
