CHAPTER VI 



THE INTERNAL ECONOMY OF THE BIRD's BODY 



§ I. The Master- Activities. § 2. Muscular Activity. § 3. Nervous 

 Activity. § 4. The Sustentative Functions. § 5. Respiration. 

 § 6. Excretion. § 7. The Uses of the Blood. § 8. Warmblooded- 

 ness. § 9. The Regulatory System and the Resulting Correlation. 



A VORTEX-RING from the chimney of a locomotive or a 

 smoker's mouth persists for some minutes in its atmospheric 

 environment. A whirlpool in a river remains the same for 

 years though its actual material is changing every second. 

 A living creature is also a wondrous eddy of vortex- rings, 

 enchanted into unity ; and physiology is an inquiry into this 

 enigma of persistent integrity in spite of ceaseless change. 

 The aim of this chapter is to illustrate what we may venture 

 to call the orchestration of the bird's body — and does it not 

 find its highest expression in the music of Spring ? 



§ I. The Master- Activities 



It is plain that there are two master-activities in the 

 animal body, namely, moving and feeling, the functions of 

 the muscular and the nervous system respectively. To 

 promote these two functions, often termed contractility 

 and irritability, is the task of all the other everyday functions, 

 such as digestion, respiration, and excretion. They are 

 sustentative, or subsidiary, or auxiliary ; they are not ends 

 in themselves like moving and feeling. The reproductive 

 function is in a different category. 



At the same time, it must be admitted that there is a 

 very real sense in which the alimentary system commands 



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