78 RESPIRATORY MECHANISMS 



and to calculate the necessary metabolism and the amount of 

 heat to be eliminated. The results, which must necessarily be 

 very approximate, do indicate that during rapid flight the 

 metabolism must be very greatly increased. A pigeon flying, 

 say, at a rate of 70 km = 43.5 miles per hour would have to 

 spend 14.8 Cal in overcoming the resistance. With a 25% 

 utilization of the metabolic energy this should correspond to a 

 metabolism of 2.3 (the resting value) + 59.2 Cal/hour or 

 26.8 times the resting value. It appears that a higher rate of 

 ventilation is necessary to get rid of the extra heat generated 

 than to obtain the necessary oxygen, and Zeuthen concludes 

 that during flight the ventilation of the air-sacs is increased 

 beyond that of the lungs. It will be interesting to have these 

 theoretical deductions verified by actual experimentation. 

 At present it is possible only to affirm that animal flight means 

 a stress both upon metabolism and upon heat dissipation 

 greater than any other form of muscular work. 



It seems to be a general rule, holding also for bats (v. Saal- 

 feld, 1938) and for many insects, that during flight, respiration 

 is synchronized with the wing movements. 



The respiratory and circulatory adaptations to diving. A number 

 of the air-breathing vertebrates are able to dive, and some are 

 able to stay under water for quite a long time. This ability 

 raises interesting problems concerning their respiration about 

 which we could until recently only make guesses. Thanks 

 mainly to the work of Irving and Scholander we are now in a 

 better position, and some points regarding the respiration of 

 diving animals have been made tolerably clear. 



Long-time divers are found in all the vertebrate classes. 

 The Amphibia can remain very long under water, thanks to 

 their cutaneous respiration, but in all the others the uptake of 

 oxygen through the skin is insignificant. 



Sea snakes are reported (Curran and Kauffeld according to 

 Volsoe, 1939) to remain submerged for at least 8 hours and 

 have been caught at depths up to 30 meters. 



