41 



the screen freezing up from insufficiency of water, which 

 only occurs at a more advanced period of the frost) ; the 

 stoppage, moreover, is temporary, for as soon as the tem- 

 perature rises, or the stream freezes entirely across, the 

 cause is removed, and the water soon clears the passage 

 for itself, but in this lies the very essence of the danger, 

 namely, that the water may have been off the works for a 

 few hours, and the eggs exposed to frost, and in the morn- 

 ing everything seems as usual, and the cause of the eggs 

 dying, perhaps a week afterwards, entirely unsuspected. It 

 is not advisable to place any hake or screen guarding the 

 inlet perpendicular to the water, as leaves, &c., will collect 

 in great quantities, and although fir branches laid in front 

 generally prevent the water being entirely cut off, the 

 amount of cleaning and watching is considerable, and a 

 certain risk will always exist. 



A leaf screen made of perforated zinc laid nearly 

 parallel with the surface of the water is probably the safest 

 way of making a connection with an open river ; if pro- 

 perly placed, any debris collecting on the screen, so soon 

 as it begins to reduce the flow, is washed off by the upper 

 current, and the supply after having passed through the 

 zinc screen can be led into a small collecting well, and 

 thence piped to the Hatching-house. 



The Hatchery itself should be substantially built on 

 sound foundations, brick and concrete being probably the 

 best materials to use ; ventilation, light, and protection 

 from frost are the principal objects in construction ; and 

 above all things the drains must be sufficient and rat-proof. 

 Keeping these points in view, the situation of the Hatchery 

 should be governed by the water supply. The house also 

 should be as large as possible, as very much better work 

 can be done in a few central establishments than in many 



