26. It should give the bees the means of ventilating their hives, without enlarging the entrance too much, so as to expose them to moths and robbers, and to the risk of losing their brood by a chill in sudden changes of weather. (See Chapter on Ventilation.) To secure this end, the ventilators must not only be independent of the entrance, but they must owe their efficiency mainly to the co-operation of the bees themselves, who thus have a free admission of air only when they want it. To depend on the opening and shutting of the ventilators by the bee-keeper, is entirely out of the question. 27. It should furnish facilities for admitting at once, a large body of air; so that in winter, or early spring, when the weather is at any time unusually mild, the bees may be tempted to fly out and discharge their fæces. (See Chapter on Protection.) If such a free admission of air cannot be given to hives which are thoroughly protected against the cold, the bees may lose a favorable opportunity of emptying themselves; and thus be more exposed than they otherwise would, to suffer from diseases resulting from too long confinement. A very free admission of air is also desirable when the weather is exceedingly hot. 28. It should enable the Apiarian to remove the excess of bee-bread from old stocks. This article always accumulates in old hives, so that in the course of time, many of the combs are filled with it, thus unfitting them for the rearing of brood, and the reception of honey. Young stocks, on the other hand, will often be so deficient in this important article, that in the early part of the season, breeding will be seriously interfered with. By means of my movable frames, the excess of old colonies may be made to supply the deficiency of young ones, to the mutual benefit of both. (See Chapter on Pollen.) 29. It should enable the Apiarian, when he has removed the combs from a common hive, to place them with the bees, brood, honey and bee-bread, in the improved hive, so that the bees may be able to attach them in their natural positions. (See directions for transferring bees from an old hive.) 30. It should allow of the easy and safe dislodgement of the bees from the hive. This requisite is especially important to secure the union of colonies, when it becomes necessary to break up some of the stocks. (See remarks on the Union of Stocks.) 31. It should allow the heat and odor of the main hive, as well as the bees themselves, to pass in the freest manner, to the surplus honey receptacles.