THE NURSERY. 85 



finally kill them. Again, by compelling the young 

 fish to head up against a current, you not only keep 

 them healthy, but can even sometimes save their lives 

 when they have become sickly, and would otherwise 

 have died. 



The way to raise hardy, healthy trout is to put the 

 young fry in a current, and keep them strong enough, 

 by feeding, to make them feel like heading up 

 against it. 



3. Protection against too forcibk suction through the 

 outlet. If the pressure against the screen is too vio- 

 lent, the fish will be sucked against it, and cannot 

 keep off. A very wide screen is the protection against 

 this, or, if necessary, a dead-water board, nailed on 

 below the screen. 



4. Security from overflow. When sudden showers 

 come up, especially in the early summer, the streams 

 will collect so much fine floating matter as to clog up 

 the screens very rapidly. 



A very little of the green Conferva, sometimes 

 called frog-spittle, will give a great deal of trouble 

 from this cause. Various other circumstances also 

 make it important to take especial pains to guard 

 against an overflow. This is accomplished by having 

 deep sides to the rearing box, and by the use of wide 

 screens. Sometimes, in order to obtain perfect secur- 

 ity, it is found necessary to insert a long narrow screen 

 in the side of the box, near the top, called a safety 

 screen. This, with the regular screen at the outlet, 

 will usually take the water off sufficiently fast when it 

 rises to the safety-screen level. 



