IX 

 CONCLUDING REMARKS 



The literature concerning respiratory mechanisms from mor- 

 phological, physiological, and oecological points of view is very 

 large, and no attempt has been made in the preceding pages 

 to cover it, but rather to give representative examples of the 

 ways in which the problems of respiration and especially of 

 the oxygen supply have been solved in the animal kingdom, 

 and to arrange these examples into a kind of physiological 

 system, built up on analogy of function. It has been at- 

 tempted to show how the solutions reached are governed by 

 physical and chemical conditions and how quantitative formu- 

 lations of ideas and theories are necessary to bring out the 

 salient features. 



It is hoped also that this presentation may serve as a stimu- 

 lus to further studies, and it may be appropriate to indicate 

 certain lines along which research is desirable and will prob- 

 ably be fruitful. 



One such line is the study of ventilation regulation as in- 

 fluenced by varied concentrations of oxygen and CO2. It is 

 essential in such studies that the animal be held or confined 

 without being cramped or disturbed — in many cases a light 

 narcosis may be very useful — and it is necessary not only to 

 count or record respiratory movements, but to obtain quantita- 

 tive measurements of the ventilation. In many studies, even 

 quite recent ones, the mistake has been made of using C0 2 

 concentrations much higher than those which can be en- 

 countered in nature, with the result that the regulating 

 effects have been missed entirely and only the narcotic effect 

 observed. 



An important but difficult line of attack is to study metabo- 

 lism and respiratory mechanisms under stress. In some cases 

 exposure to low oxygen concentration will be adequate as a 



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