ACCLIMATISATION AND BREEDING 209 
building, opens into a passage which turns abruptly and so ex- 
cludes the possibility of draughts. The doors can then be 
left wide open day and night, summer and winter, nor is any 
artificial heating arrangement required. The animals obtain 
the benefit, however, of what I may call a natural heating 
Lions in the snow. 
arrangement. This is effected by allowing their dung to 
accumulate on the floor to the depth of about a foot. It is 
covered daily with fresh straw; but the warmth given out by 
the process of decomposition keeps the building at a tempera- 
ture considerably higher than that which prevails outside. 
With the carnivores also, similar experiments have 
been undertaken ; and they have been attended with similar 
14 
