_Hygienic measures of Bees._--Among the animals who expend industry on hygiene and the protection of their dwellings, we must place Bees in the first line. It may happen that mice, snakes, and moths may find their way into a hive. Assaulted by the swarm, and riddled with stings, they die without being able to escape. These great corpses cannot be dragged out by the Hymenoptera, and their putrefaction threatens to cause disease. To remedy this scourge the insects immediately cover them with _propolis_--that is to say, the paste which they manufacture from the resin of poplars, birches, and pines. The corpse thus sheltered from contact with the air does not putrefy. In other respects Bees are very careful about the cleanliness of their dwellings; they remove with care and throw outside dust, mud, and sawdust which may be found there. Bees are careful also not to defile their hives with excrement, as Kirby noted; they go aside to expel their excretions, and in winter, when prevented by extreme cold or the closing of the hive from going out for this purpose, their bodies become so swollen from retention of faeces that when at last able to go out they fall to the ground and perish. Buechner records the observations of a friend of his during a season in which a severe epidemic of dysentery had broken out among the bees, which interfered with the usual habits of the insects; on careful examination of a hive it was found that a cavity in the posterior wall of the hive, containing crumbled clay, had been used as an earth closet. Many mammals are equally careful in this respect; thus, for example, the Beaver, as Hearne observed, always enters the water, or goes out on the ice, to urinate or defaecate; the faeces float and are soon disintegrated. Animals are also careful about aeration. Thus, among Bees, in a hive full of very active insects the heat rises considerably and the air is vitiated. A service for aeration is organised. Bees ranged in files one above the other in the interior agitate their wings with a feverish movement; this movement causes a current of air which can be felt by holding the hand before the opening of the hive. When the workers of the corps are fatigued, comrades who have been resting come to take their place. These acts are not the result of a stupid instinct which the Hymenoptera obey without understanding. If we place a swarm, as Huber did, in a roomy position where there is plenty of air, they do not devote themselves to an aimless exercise. This only takes place in the narrow dwellings which Man grants to his winged guests.