DEFENCE AND SANITATION OF DWELLINGS. 237 



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. Buchner 

 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 examina- 

 tion 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 fzeces 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 



