80 RESPIRATORY MECHANISMS 



Table 8 



age to 15%, while the oxygen dropped to 4%; conditions 

 which the bird would tolerate and which show an unusual 

 resistance against C0 2 . In experiments involving the respira- 

 tion of gas mixtures poor in oxygen it was shown that the birds 

 would stand breathing 5-6% O2 for a long time, while taking 

 up much less 2 than normally and eliminating either the 

 normal quantity or an excess of CO2. Given gas-mixtures with 

 less than 1.5% 2 the bird would be killed just as rapidly as 

 non-divers and would lose oxygen from the blood to the air. 

 Bohr ascribes this last result to a harmful action on the lung 

 tissue, but damage to the central nervous system is a much 

 more likely explanation. 



Among mammals the greatest divers are the whales and 

 among these again the sperm whale and the bottlenose seem 

 to have the records for depth (about 900 meters) and endur- 

 ance (1-2 hours) according to a valuable collection of data by 

 Irving (1939). How is this possible? 



The whales, especially the large ones, do not lend themselves 

 willingly to experimentation, but very suggestive information 

 has been obtained on more manageable animals like the seals, 

 the beaver, and others. 



The first point I would like to make is that in true diving 

 animals of all classes contact of the respiratory openings with 

 water stops breathing by reflex. 



During the period of submergence COo accumulates in the 

 blood and would in terrestrial animals (at least in mammals) 

 force the resistance against respiration, but it seems to be a 

 general rule for divers to be much less sensitive to CO2 as 



