The washing and feeding should be repeated several times a day, and in about a week a little more calomel should be given, and afterwards flowers of sulphur. This treatment will soon effect a cure. LETTER XVI. THE INHABITANTS OF THE PONDS: FISH; AND AQUATIC FOWLS, INCLUDING SWANS, EXOTIC GEESE AND DUCKS.--INHABITANTS OF THE WOODS: INCLUDING PHEASANTS AND PARTRIDGES, HERONS AND BITTERNS.--AVIARY.--APIARY, AND THE MANAGEMENT OF BEES.--SILK-WORMS. When a fish-pond is to be made, a situation should be chosen where there is a natural hollow, so that the ground which is to form the bottom of the pond may be as little disturbed as possible. If this situation be near a river so that a feeder may be led into it, nothing else is wanted to form a fish-pond but an embankment and a sluice, and these you must have made by persons used to such employments. It is necessary, however, to take care that the pond is fed from a river, as spring water is not only too cold for the fish, but is seldom quite free from mineral substances. The pond should be made at least six feet deep, and if twelve feet or more it will be better for the fish: as in frosty weather they will remain near the bottom, and will find enough air in the great body of water above them to enable them to live a long time after the surface is frozen over; while, on the contrary, if the pond be shallow, the fish will soon exhaust all the air it contains, and will perish unless the ice be frequently broken, to admit air from the atmosphere. In shallow ponds, also, the rushes and other weeds grow so fast as to occasion considerable expense and trouble in having them cleared away.