BREATHING OF MAMMALS 123 



lung-breathing animals save unheeding men ; and to 

 purify the air, which for ground animals, such as 

 mammals are wont to be, is too harsh or spore-laden 

 for immediate diffusion in the lungs, this nose is 

 elaborated within and without. Its chambers are 

 subdivided by a scroll-work partition that converts 

 them into labyrinths. Inspiration through such tubes 

 now becomes more effective at the outset ; and as the 

 wash of air whisks round the corners it deposits some 

 of its impurities on to the soft membrane that lines 

 them, and from the middle part of the nasal passage 

 the air, toned, purified, and warmed, goes to the 

 diffusion-chamber. 



The maintenance of activity in mammals, though 

 less impressive than in birds, comports well with their 

 needs. More groundlings than these, their quest for 

 food is more deliberate, their meals heartier and 

 with temperate intervals. Their reserves of strength 

 and material are greatly in excess of immediate needs. 

 The combustion changes of their muscles and glands 

 furnish abundant heat, whether by the patent or hidden 

 activity of these organs, which is evidenced by the 

 dark colour of their flesh. Protected by both fat 

 and hair, this heat is but slowly lost, and the relation 

 of gain to loss is regulated by a nervous control that 

 is centred in the capacious brain. So accurate is 

 this adjustment that man and beast preserve their 

 several temperatures under hot, cold, and changeable 

 climates, and thereby ensure that continuance of 

 activity which is one reason for their dominance. 



