PARTS AND FEATURES 



He considered that the lung capacity of the porpoise was about the 

 same as in man, but it is Hkely that in a cetacean of strictly comparable 

 size it is somewhat greater. At least all investigators are apparently in 

 agreement that aquatic mammals have a greater lung capacity than ter- 

 restrial ones of the same size. 



The above facts indicate that not only can the porpoise retain air in 

 the lungs entirely independent of the muscles of the thorax or dia- 

 phragm, but the oxygen can be more completely utilized by the lungs 

 themselves. Not only this, but the blood of cetaceans and pinnipeds at 

 least is richer in hemoglobin than usual, and hence can store more oxy- 

 gen. In addition the intrinsic musculature of the lungs and the character 

 of the diaphragm enable them to empty the lungs more completely, and 

 the pressure at considerable depths also facilitates the absorption of all 

 oxygen. 



The physiology of normal respiration is too involved to present here 

 and may be obtained from any good text book. Certain points must be 

 considered briefly, however. The respiratory apparatus of man is not 

 particularly efficient. Thus, about 20 per cent of the air which we 

 breathe is composed of oxygen, but in normal, unlabored breathing we 

 utilize only about a quarter of this amount. If nitrogen be added so that 

 the oxygen be reduced to 10 per cent the respiratory rate will be slightly 

 raised, and pulse accelerated, but there is no definite discomfort felt. 

 When the oxygen content is gradually reduced to 6 or 7 per cent, how- 

 ever, consciousness is lost, often without much of a premonitory symp- 

 tom. Thus, in spite of rapid respiration, we are incapable of making 

 much use of one-third of the oxygen that is furnished us. It is likely 

 that whales can use almost all of this. 



The total lung capacity of the average man is supposed to be about 

 4,700 cc. During quiet respiration only about 500 cc. is taken in, and 

 in spite of our best efforts we are unable to empty the lungs of their 

 final 1,000 cc. It is likely that the whale almost completely fills the 

 lungs at each inspiration, and disposes of practically all the residual air 

 at each expiration. 



In man the expired air usually contains about 4 per cent of carbon 

 dioxide. When the CO, content of the inspiration is raised to even 1 

 or 2 per cent increased breathing results to a marked degree, and at a 

 content of 10 per cent there is great distress experienced and the face 

 becomes congested, while the respiration is multiplied quantitatively sev- 

 eral fold. It has been said that the breath cannot be held voluntarily 

 after the carbon dioxide content of the lungs has passed 7.5 per cent at 



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