176 How to obtain it. 
change of water that has been provided, and if the current be all 
on the surface, it is clear that it would not be advisable to bury 
the eggs deep in the gravel. The best plan, in such a situation, 
is to place them on the surface, slightly mixed with the gravel, 
which prevents them from touching one another. When it is 
remembered that every egg gives off carbonic acid, the advantage 
of this will be apparent. 
Some years ago I invented an artificial hatching bed, which 
has now been thoroughly tested and found to work exceedingly 
well. It is made of wood, has a lid, and is on the hatching-box 
principle. In size, it has been found convenient to make these 
beds twelve feet long, nine inches wide inside, and five or six 
inches deep. Along the entire length of the box, except for about 
two inches where the water enters, is fixed a false bottom of 
perforated zinc. The inflowing water is conducted under this 
perforated bottom, by means of a water-board placed a couple of 
inches from the end where the water supply enters. The perforated 
bottom is placed about an inch above the real bottom, and the 
water rises up through it. It is coated with asphaltum varnish, and 
covered with gravel, and upon this gravel the eggs are deposited. 
At the lower end of the box is the outlet for the escape of 
the water. This is formed by simply cutting away the upper 
portion of the box end, say for a couple of inches down. It will 
be clearly seen from this description that the water on. entering 
the box at one end is conducted direct to the bottom, but passes 
out at the top, so that it must rise up through the perforated 
metal and the gravel and eggs upon it. 
Gravel is beneficial in several ways. It tends to prevent over- 
crowding of the eggs, and it keeps them from coming in contact 
with the metal. It also provides a more natural bed for the 
“alevins,” and as we are now endeavouring to treat them as nearly 
according to nature as possible, it is best that it should be so. I 
have always liked to associate young trout with a clean gravelly 
bottom as far as practicable, but in a large hatchery, where quan- 
tities are dealt with, it is much better not to use it at all. The 
fish do better and are kept cleaner when they are the sole occu- 
pants of the rearing box. But in an artificial bed the case is very 
different. In the rearing box in the hatchery the fish are obliged 
